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A Chekhov's Gun is an item introduced before its use, and is usually quite inconspicuous. In a movie, if you see a brief shot of a single object, such as a fork on a table, you can be guaranteed that that particular item will be used later in order to resolve a problem or as a weapon. The item's function may or may not be fully apparent at first and discovering its use may be part of the narrative device.
Chekhov's Armoury is when the writer uses several (and in some cases, uses too many) Chekhov's Guns, not all of which are painfully obvious. (Skilled writers may give the painfully obvious ones trivial uses, and use them chiefly to disguise the minor ones.)
The Law of Conservation of Detail taken to its Logical Extreme.
Carefully written and/or Myth Arc-laden shows tend to have a Chekhov's Armoury. It also provides good potting soil for Epileptic Trees. Opposite of Cow Tools, where there are a large number of seemingly significant tchotchkes which turn out to be just window dressing.
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Anime & Manga
A lot of stuff in Mahou Sensei Negima!!, especially regarding Asuna. Notably, all of the times the spells Negi cast on her fail is not due to him being an Inept Mage, but rather due to her Magic Cancel ability. Her poor grades are implied to be caused by a large scale Laser-Guided Amnesia spell. Plus a bunch of other stuff.
Mahou Sensei Negima!!'s Armoury was especially effective because much of the foreshadowing was disguised as comedy, once again especially with regards to Asuna. Her superhuman speed, strength, and agility were mostly played for slapstick humor, her Magic Cancel was mostly played for fanservice (so that Negi's spells would blast her clothes off but leave her unharmed), and so forth.
Also, while not necessarily an example of Chekhov's Armoury per se, it's also interesting to pay attention to how Akamatsu handled the fighters and supernatural characters in the earlier chapters. For example, the characters who were left out of the Dodgeball gamenote All of them, excepting the cheerleaders, are extreme BadAsses who could have won the match singlehanded. The most extreme of these foreshadows was the class roster in the first chapter.
The earliest is Luffy's hat; in the anime, its importance isn't explained until after Zoro joins the crew, as opposed to chapter one in the manga. But after the Time Skip about six hundred chapters later, it's revealed that Shanks treasured it so much because he got it from his former captain, Pirate King Gold Roger.
Then there's Coby, who accompanies Luffy for the first couple of episodes and chapters before he joins the Marines. He becomes a chore boy, but eventually becomes an apprentice to Vice-Admiral Garp, who was famous for having cornered Gold Roger many times. It turns out that Garp is Luffy's grandfather.
Nami's first canon appearance has her mentioning to Luffy that she needs 100,000,000 berries (the currency used in that world, not the fruit), and that she hates pirates because a pirate killed someone dear to her. It's revealed at the end of the first saga that that same pirate, Arlong, took over her village and enslaved her, striking a bargain to let them all go if she paid him 100,000,000 berries. And he valued money so much that he never goes back on any promises that involve them. Unfortunately, that doesn't extend to using Loophole Abuse...that is, unfortunately for him, when Nami, reduced to tears, begged Luffy for help. Arlong learned his lesson.
Guess what Luffy's bounty is worth? 300,000,000 berries. Three times the amount she needed.
And then we have Arlong's Dragon, who reappears a few hundred chapters/episodes later, and becomes the Straw Hats' friend and ally.
Laboon and Crocus, an oversized whale and an extremely skilled doctor at the entrance to the Grand Line. Laboon befriended a group of pirates that promised to return to him after they navigated the Grand Line, but they never show. Crocus left as a ship's doctor to find out what happened to them, and informs Laboon that they ran away. Laboon didn't want to believe him. It eventually turns out that it wasn't true; they were, in fact, killed. But one of the crew members, the acting captain Brook who happened to be Laboon's favorite, ate the Yomi Yomi no Mi/Revive-Revive Fruit, which enabled him to return to life. He is currently traveling with the Straw Hat Pirates as their musician, in order to fulfill his crew's promise. Oh, and Crocus? He was Gold Roger's doctor.
Little Garden. Two giants have been fighting for a hundred years, their every battle ending in a draw. The fact that the Straw Hats manage to befriend them is no surprise. The surprise comes a couple of hundred chapters later (notice a pattern here?). Oimo and Kashi, giants and gatekeepers for one of the World Government's bases, Enies Lobby, became so because the World Government told them that they had their bosses in prison, and promised that if they could guard the gate for a century, they would allow them to go free. When the Straw Hats manage to break the gates, and Oimo tearfully tells Usopp his story, the latter informs him of the truth, resulting in a pair of powerful Heel Face Turns.
Hyouka is nearly defined by this trope. Wth very few exceptions, every aside and piece of background chatter in an episode comes back, at some point or another, as a piece of whatever puzzle the club is trying to figure out.
In My Little Pony Micro Series Issue #3 pretty much everything behind the wellness center and what Rarity uses to save it is shown as background images (the "Goops for Stuff" stand, the waving Filthy Rich billboard) or seemingly dropped in in dialog.
Justified in Phil Foglio's Stanley and His Monster miniseries: When Stanley has to go to he— a bad place to rescue the Monster, Ambrose Bierce has him pick "Everything he thinks they will need", simultaneously casting a spell that creates a causality loop in which whatever Stanley picks will be exactly what's required.
Films — Live Action
In The Punisher (2004), Frank Castle puts together a very impressive armory including several hidden weapons for emergencies, and a tricked out car. Every single weapon gets used, even a butterfly knife he confiscates from some punk who was harassing his neighbor. Every weapon is shown beforehand either in a montage or as part of a scene.
Everything from the now-infamous icing problem, the arc reactor's "Something Big For 15 Minutes Guarantee", right down to the flares plays a part in Iron Man.
In Iron Man 3, Tony Stark's enormous armory of suits is briefly seen (while shadowed) in one scene. In the Final Battle, he summons it to help him fight the Extremis soldiers.
Die Hard is packed to the gills with material from the Armoury. The lighter that John finds, the question "Who gives a fuck about glass?", the explosives, the Twinkies... if it shows up on screen, it gets used again. And, in some cases, again and again.
In Bruges (it's in Belgium), everything, from the type of bullets bought by Harry, to the movie Jimmy is starring in, etc., comes into play in the finale.
James Bond always seems to use every gadget in his arsenal precisely once.
That's only because they always get blown up as SOP.
But it is so rare for any gadget he gets with an explanation not to be used, that he should have bribed Q to only explain him about gadgets that "will allow you to safely take out unsuspecting enemies from a great distance" instead of those that are "short ranged, one shot weapons which will not be noticed by the enemy, and you can use as a last resort when captured, bound and being tortured".
Q is the prototypical Chekhov's Armourer.
Parodied by Eddie Izzard in one of his routines. "Q, I had a lot of stuff I didn't bloody use! The watch that turns into a hamster, what was the point of that?"
"These pants, press this button, they turn into jam. Why? The hat that turned into a bicycle, that was very funny..."
Die Another Day had a gadget that was, in fact, used twice. Bond uses the ultrasonic ring to get out of a situation in an elevated greenhouse, and again to get Jinx into his car quickly.
Subverted by the BMW in Golden Eye - though Q goes into detail about the car's "usual refinements," none of its gadgets are ever used, and the car itself makes only a cameo appearance. Product Placement at its finest.
Surprisingly, Paul Blart: Mall Cop. Absolutely everything from the comedy half of the movie makes an appearance when Paul is fighting back against the robbers. Even the hot sauce.
Well, not so surprisingly — it's a beat-for-beat, almost shot-for-shot parody of Die Hard.
Paycheck, both the original story, and the John Woo film. To be fair, it's not a side effect, this trope is the basis for the whole film.
Almost every single wish made in Shorts (and Helvetica's science project) is used in the final "short" in the fight against Giant Mecha Mr. Black, including the Bipedal Crocodile Army, the Super-Smart Baby, the germs, the aliens, the dung beetle...
In the live-action Macaulay Culkin version of Richie Rich, every single invention introduced by lead staff scientist Professor Keenbean comes back to serve the plot in some way.
In Escape from L.A., Snake is given a number of items, including an ordinary pack of matches. He uses everything given, including the matches, to light his cigarette in the total darkness once all of the world's electricity has been eliminated.
In Pee-wee's Big Adventure, Pee Wee's trip to the magic store serves as one of these. Everything he buys ends up getting used except for the boomerang bowtie, and that's only because the scene was deleted.
James Cameron's Avatar: almost every creature seen throughout the film fights in the final fight. The Toruk, the viperwolves, the thanator, etc., everything is foreshadowed, in addition to Eytukan's bow and falling from a great height.
Untraceable does this with quite a few things. Amongst them are blinking in Morse Code, a rototiller, and a car with OnStar. All of those moments almost feel like throwaway scenes, but then they all come into play in the latter half of the movie.
In the beginning of Used Cars a Mexican guy who supplies them with cars says he has a ton of them just sitting around (there has to be at least 250 in a picture he shows them). Later in the movie a driver's ed teacher, who they sold crappy cars to, is angry because now his 250 students can't learn to drive. At the end of the movie the lot is being sued for false advertisement (due to the bad guy messing with an ad to say they have a mile of cars then paying off "experts" to say it wasn't tampered with). A mile of cars is said to be about 250 cars and if they don't have that many at the lot when the judge comes by to see they lose. Remember how the Mexican had at least 250 cars and how the teacher had 250 students?
My Girl has a whole bunch, including the child-sized coffin, Vada's mood ring, Thomas J's allergies, and the fact that Vada lives in a funeral home.
The weapons the brothers end up buying in The Boondock Saints all get used right down to the "stupid f—king rope" and "rambo" knife. A LITERAL Chekhov's Armory.
An extremely literal example in Transformers: Dark of the Moon. Optimus Prime has taken to lugging around a trailer to match his trailer-truck vehicle form. The trailer transforms into a small armory of equipment he might need, such as jets, sword and shield, and more guns. Every one of these becomes important later on.
In Johnny English Reborn, anything that comes up in the first 10 minutes of the film is useful later on. e.g Taking a kick to the jewels without feeling pain, the mind controlling the body, him having the experience that age brings as opposed to the energy of youth, etc.
Clue. Even seeming throwaway gags are secretly plot-relevant.
"Red Eye" has many of these dropped into the plot within the first ten or fifteen minutes that become significant when Cillian Murphy's character begins to blackmail Rachel Mc Adams's character.
Constantine. Almost every object that Constantine receives from Beeman turns out to be useful later. The dragonbreath weapon is used by John against Balthazar twice, the two holy water ampoules are used to (a) return Constantine from Hell and (b) eat away Balthazar's face so John can beat him up with the gold knuckles, and the Amityville screech beetle is used to disrupt the demon that attacks Constantine on the street. Even the bottle of cough syrup is shown being drunk by Constantine later. The only thing that isn't used are the bullet shavings from the assassination attempt on the Pope.
The first Back to the Future is absolutely riddled with these, with almost everything significant in 1985 coming back in 1955; the last day Doc puts in the time circuits,note It is the day he came up with the flux capacitor, which Marty uses to win Past!Doc over. Marty's band wanting to play at the dance,note His guitar playing comes into effect when he plays at the 1955 dance. Jennifer's phone number,note Written on the otherwise unwanted note about the exact time the clocktower was struck and Lorraine's love storynote Explains how Marty nearly erases himself, and tells him how to make them fall in love again. are just a few examples of very important (but seemingly minor) details.
Odin's trophy room in Thor contains the Asgardian Destroyer that Loki sends after Thor while he is exiled on Earth. However, keen-eyed fans have also noticed other significant items in the trophy room that hint at the future of the Marvel Cinematic Universe. This includes:
The Infinity Gauntlet, which has been associated with the villain Thanos. Thanos was later confirmed as the Bigger Bad to Loki in the credits of The Avengers.
The Orb of Agamotto, an artifact that belonged to Dr. Strange in the comics. Marvel Studios has announced that a Dr. Strange film is currently in development.
Also occurs in the weirdest way (it's Douglas Adams after all) in the sequel, The Long Dark Tea-Time of the Soul. Needless to say, Norse Gods and a somewhat popular song are involved in the apparent suicide by beheading of some dude. Also, Dirk's non-working fridge? That has something to do with it as well.
The Dirk Gently books embody this trope really because they are all about the interconnectedness of everything. Chekov's Armoury isn't just a device Adams used, it's what he based the whole book on.
The Dresden Files, and about half of them were all introduced at the same event, Bianca's party in Grave Peril.
The Harry Potter series. Everything is a Chekhov's Gun. Everything. If you hear about a cabinet, a love potion, a locket, a snitch- chances it will turn up, often books later, as a plot point.
The longest-spanning one being the Snitch that Harry caught in his first ever Quidditch game. It appeared about halfway through the first book, was never even MENTIONED again until near the beginning of the last book. While it was around, it's true purpose wasn't fulfilled until three chapters before the end of the entire book: It held the Resurrection Stone.
The Commonwealth Saga uses this trope. Anything introduced at all will have some factor later on. Anything. If not in that saga, then in The Void Trilogy (set a few thousand years after).
Mistborn. Sweet Crystal Dragon Jesus. By the end of the third book, so many seemingly insignificant conversations, objects, and so on wind up being absurdly important. The biggest is probably Vin's earring, but there are others.
The author, Brandon Sanderson, is fond of this. Both Elantris and Warbreaker, have fully stocked armories of their own. The Way of Kings is the first book of a ten book series and has already had a number of Chekhov's Guns that were fired, and many other things that are probably loaded Chekhov's Guns that will fire in future books.
Justified in My Father's Dragon, which has a kid pack up a backpack full of ordinary kid stuff, like whistles and sticks of gum, and set out on a mission to rescue a dragon. You guessed it: everything he has in his backpack gets used at one point or another. He was advised to bring all that by a stray cat, who told him about the dragon to begin with, having travelled to its island where it was held.
The numerous things the five defecting stormtroopers in Allegiance find in the ship they stole.
Matthew Reilly's books. If it gets mentioned, it will be important later on. No exceptions. This includes things like weapons, tools, notes, furniture, dead bodies, building layout, machinery, debris, idle conversation... His books aren't compared to Die Hard for nothing.
A usual for the Alex Rider series, except subverted in Snakehead when the jungle survival belt gets taken away by the book's villain without it being used.
The Kingkiller Chronicle, to the extent that you really have to read it three times to catch all the little details that end up being important. At the point that the narrator glosses over a shipwreck as irrelevant to his story, you realize how important all those little children's rhymes are.
Lois Mc Master Bujold is amazing at this. In the Vorkosigan Saga, If Miles makes a joke about something, you can be sure that it'll have a deadly serious use later in the book. In the most epic example, in the eighteenth story Lois reaches all the way back to book 5, and a simple couch, to shame Kareen's parents, who apparently conceived Kareen on that very piece of furniture in the middle of a war, into letting their daughter persue a less frantic adulthood.
Live Action TV
Buffy the Vampire Slayer, season 5. If it shows up, even in what you think is a breather episode, it matters in the big finale against Glorificus. In particular, the supposed breather episodes introduced the Buffybot and the troll hammer, both of which were crucial in the season finale.
The point where Spike calls Xander a 'glorified bricklayer'. Also relevant for the big fight against Glory. Or the message the First Slayer gives Buffy back at the end of season 4.
Jericho, in a manner of speaking, has a Chekhov's Armoury: In episode two, Robert Hawkins is seen mysteriously unpacking weaponry into a location of storage. It isn't until 18 episodes later when this cache of weapons is used to fight a frickin' war. May also be Someday This Will Come in Handy..
LOST. The hard part is figuring out which ones are Chekhov's Guns, which are Red Herrings, and which are something else entirely.
MacGyver. Just take a look around the room, remember what he has in his pockets, oh, and that tennis racket you were holding for your son. Yeah, now let's go disarm a nuclear warhead.
Spooks: In the episode "Love and Death", Danny and Zoe are send to intercept a scientist, with a briefcase full of documents and a false bottom containing the kit to asassinate him if that doesn't work.
Averted in the "apartment scenes" at the beginning of most Mission: Impossible episodes. Every unusual item and skill needed for the plan is showcased, mostly so they'll be familiar to the viewer when they're used later.
Absolutely everything in Stargate SG-1. People, events, pictures of people, the whole thing. Jolinar knew something. There's two Stargates on Earth. They can overload their Stargate to shunt the connection to another one. Teal'c carries a big staff weapon normally on offworld missions. Apophis died on camera. The Asgard are floating about the place. The Reetu are invisible, and the Tok'ra have invisible Reetu detection guns, which they gave to the SGC. One shot from a Zatgun stuns, two kills. That's not including the solid Stargate fact that every single piece of Earth mythology regardless of age or culture will definitely turn out to be alien in origin, with most gods being Goa'uld.
Stargate Atlantis: Remember that one-off story in the early seasons about a drug that had a 50% mortality rate but made the survivors immune and poisonous to the Wraith? It was deemed unethical and never mentioned again? It forms the crux of the plot in seaons 4 and 5, after the drug is found and weaponized against the Wraith by Micheal and alters the entire balance of power in the galaxy.
And what about the Wraith enzyme's addictive properties? Dr. Beckett's occasionally mentioned anti-Wraith retrovirus? That Ancient personal shield that makes one invulnerable?
It even has some cross-series examples: the Anti-Replicator Guns and Asgard Plasma Beams both feature heavily in Atlantis after being introduced in SG-1.
Stargate Universe is a more solid example, as the show has only run for two seasons, with an extremely tight continuity. And there's no telling how many guns didn't get to go off due to the show's cancellation. A few examples:
Eli documenting everything with the kinos: used to make an Apocalyptic Log in "Time".
Scott suffers memory bleed-through from Telford, revealing that Telford is having dinner with Young's wife, resulting in pointless drama: Rush also suffers from the memory bleed-through, revealing that Telford is working for the Lucian Alliance, resulting in Destiny getting warning of the Lucian Alliance attack at the end of Season One.
The crew vanishing through an unstable wormhole: went back in time, founded a civilization we encounter in "Common Descent"
The stasis pods Eli and Brody are fooling around with: used to save the crew when they decide to leave the galaxy ahead of schedule.
In part one of the Star Trek: The Next Generation season 5 finale/season 6 premier Time's Arrow, Data and Captain Picard are looking over all the items unearthed in the archeological dig near San Francisco. In part 2 we learn they're all left behind by Samuel Clemens and other characters. Notable are the revolver, which Clemens threatens the crew with, the pocket watch, which Clemens makes a specific point of leaving behind in the end, and Data's head.
Planescape: Torment may be the archetypal video game example. If you are prompted to pick up an item, either in dialogue or in the narration, keep that item. It will almost certainly become necessary to completing a quest days down the line.
The most notable gun in the armory is the Bronze Sphere you obtain for Pharod in the first story quest of the game. You are not prompted to get it back later, but if you do, it will only eat up an inventory space until the very last scene before the final boss. At that point, it becomes priceless, since it's a sensory stone containing memories of your first incarnation, granting you a boatload of experience and the ability to invoke the Mark of Torment.
Another big one is the Blade of the Immortal, a relatively weak weapon that is forged from a drop of the Nameless One's own blood by Coaxmetal. It's entirely possible to miss getting it, and it's not necessary to complete the game, but if you do get it, you can defeat the Transcendent One by threatening suicide, since it's the only weapon in existence capable of permanently killing the Nameless One.
The Nameless One's previous incarnations have a habit of leaving behind tidbits that help him along on his quest, whether deliberately or not. In particular, without the efforts of the Practical Incarnation and the Paranoid Incarnation, it's unlikely that the Nameless One would be able to achieve his goal at all.
Final Fantasy VIII has the Information menu, which features lots of interesting little background tidbits about the setting. A lot of it turns out to be very useful information later on. There's also a lot of early references to the orphanage in Centra, including comments about Guardian Forces causing unforeseen mental effects including memory loss, Seifer and Zell's irrational hatred of one another, Quistis's attraction to Squall, Irvine's odd behavior around Edea and Selphie, and Squall's confused familiarity towards Ellone.
In the Telltale Games Sam & Max: Freelance Police, items from previous episodes will often still be in your inventory. The only time something doesn't carry over is if it would completely change the way to solve a puzzle.
The LACK of this trope in adventure games can lead to an Empty Room Psych when the players go crazy trying to figure out what the useless inventory item is meant for.
While not revealed at the start, it's worth noting that to complete Zelda II The Adventure Of Link (at least, the way it's meant tobe played) you must get every item and every spell in the game, which means you must get every MP upgrade as well. Some of these appear to be unnecessary until you've spent a lot of effort only to find it's impossible to progress. The game itself is so minimalist that there exist no more Link Dolls than you can hold at once.
Ultima IX subverts this with Britain's Avatar Museum. It holds every puzzle-solving Plot Coupon in the history of the series, not one of which become relevant to this game.
Sword of the Stars: There are tonnes of hints about the true nature of the Suul'ka littered in the lore. It looks so obvious in hindsight.
This guy named Adam Miller who's the author of several pretty good Neverwinter Nights mods does that from time to time. (For example, an amulet that lets you speak to the dead, which you can buy from a fortuneteller towards the beginning of Dreamcatcher, is necessary for solving a side quest in Dreamcatcher 3. Also notable is a three-part rod which you need to hunt for the pieces of in the first three Dreamcatcher mods.)
In Freddy Pharkas: Frontier Pharmacist, every single item you picked up had a use. Not only that, but if you tried combining an item with another item it didn't belong with, or using it on yourself, you'd always receive a humorous response (in addition to several Non-Standard Game Over instances).
Space Quest 4 alone has a cigar butt, a laptop, a jar of corrosive slime scraped off the sewer walls, a battery-powered Energizer Bunny expy, a floppy disk, and a chewing gum wrapper be essential to stopping Vohaul's abuse of the Timey-Wimey Ball. Then again, that game also has the Unstable Ordinance...
All of the pieces of evidence found over the course of Police Quest: Open Season's storyline come into use on the final day.
In The Journeyman Project, the Wire Cutters found on Mars are used to open the fire sprinkler box in Australia and short-circuit Mercury; the Retinal biochip obtained from said robot is used to pass a retinal scanner in NORAD VI, where you also need the Oxygen Mask from Mars; the Access Card Bomb, also from Mars, is used to breach the Caldoria Heights rooftop door; and Mercury's stun gun is used to neutralize the Big Bad. The one Red Herring is the Gas Canister in NORAD, which causes a Game Over if taken.
The Court Record in any Ace Attorney game is always a Chekhov's Armoury. Nearly every item will come in handy at some point in the case, and it's generally the most innocent ones (like the parrot) who rescue you from the guilty verdict.
Sharin No Kuni has one of these. Most of its items relate to the fact that Ririko is actually there, in the scene, and she's almost always following Kenichi. It's just that no one even acknowledges her existence due to the Maximum Penalty she bears.
So much stuff in Girl Genius that the wiki doesn't even have a list. The most notable examples might be the Heterodyne it's-not-a-lamp, Agatha's broken locket, the fate of Dr. Merlot... and oh, Dear Ghu, the time windows.
8-Bit Theater has pulled the mother of all of these, a series of over 1000 comics now taking a seemingly insignificant event from one of the earliest comics and turning it into a plot device involving billions of years, the most powerful wizard in existence, and bringing back most of the major antagonists of the past 1000 comics BACK into the story for what will almost certainly be one of the comic's grand, absurdly awesome anticlimaxes.
When the characters all get their class changes, Thief says that he stole his ninja upgrade from the future. Later, when Chaos downgrades the party back to level 1, Thief is the only one left in his class change suit. For about 5 seconds. Because guess where he stole it from...
In comic 1221 it pulled quite possibly the biggest one in history at 1,214 issues long when it turnes out that despite Black mage saying that it would never work the world was saved by four 'white' mages. Brian Clevinger we salute you.
MS Paint Adventures - both Problem Sleuth and Homestuck. Nearly every single item introduced becomes relevant to the plot, or at least pops up again later. Hussie admits that a lot of his foreshadowing is done by going back and looking for stuff to make references to. He has also admitted to having at least one plot detail in store for a year.
Last Res0rt — If it's an item, pet, or person that has anything to do with one of the main characters, it's probably a Chekhov's Gun. Jigsaw's violin, Jason's jacket, Jason's dog, Adharia's bottle necklace, Daisy's leg, Daisy's autie lenses, Cypress's hair wrap...
The Whateley Universe is made of this trope. For example, nearly every single thing Phase has ever bought or acquired for her utility belt has gotten used somewhere, even if it's in another author's story. The story about Cavalier and Skybolt turning to the Dark Side and becoming The Don's servants was written back in 2004. The significance of that and what it really meant to the plots has only come out in the more recent stories, starting with "Christmas Elves". The backstory of Tennyo was introduced in the earliest stories; how it could be used as a weapon against her didn't come out for about five years.
The Whateley Weapons Fair. Most of what we saw has turned out to be important, either in that story, or later on. Jobe's whiny arrogance (and frightening competence), Delta Spike's well-earned nickname, Wunderkind and Spark's personal forcefield generators, the equipment nobody wanted to buy from Mega-Death, Kew's inventions for the Intelligence Cadet Corps, even the super-strong condoms Greasy made for superstrong students.
Practically literal with the showdown between Linkara and his alternates and Mechakara. Almost every weapon bar pokeball-captured Pyramid Head, which Linkara felt would just be too much in an already complicated battle from previous reviews is brought out, along with Black Lantern Spoony and the rarely-seen Pollo.
The players in the Global Guardians PBEM Universe were encouraged to flesh out their characters' backgrounds to the fullest extent possible precisely because they would then be used as one big Chekhov's Armory. Even characters who had backgrounds that were mysterious even to themselves found their Back Story used for plot details later.
Mother of Learning contains innumerable details in the early chapters whose importance only come to light many, many chapters later.
Ćon Flux was filled with these, although most were quite obvious.
Totally Spies!! does this every single episode, as a James Bond reference.
Leroy & Stitch had Lilo's departing gifts to Stitch, Pleakley and Jumba. Stitch's gift was a tiki necklace which allowed Lilo to identify Leroy as an imposter because he wasn't wearing it. Next was a rock given to Pleakley that was used to disrupt the event horizon of a black hole that he, Stitch and Jumba were hurtling into and allow them to escape. Finally there was the Aloha 'Oe record given to Jumba which he used to create a secret mechanism in Leroy that made him shut down if he (or his clones) heard it. This ends up leading to both a Crowning Moment and a Crowning Music of Awesome the end where Stitch, Lilo, 625 Reuben and a bunch of Stitch's cousins put on a concert to defeat the Leroy clone army at the end.
This is a staple of many cartoons aimed at very young children. Dora the Explorer, which started the trend, actually averts the trope slightly by sometimes carrying a few items she doesn't need.
Averted in The Venture Bros.. One episode has Brock Sampson going through the standard OSI mission tool kit, and throws away everything in it because they are either "gay, stupid, or never uses them."
Much like in the Dresden Files example above, large group scenes tend to introduce characters and plot points that become very significant later on, so it may at first seem like the writers are using this trope. They aren't. They've admitted when they're stuck they just go back and look at old episodes to find something to write about.
Used expertly in Rango. Roadkill and the Spirit of the West? Used to break Rango out of his Heroic BSOD. The freaky cactai? Lead Rango to the pip the mayor is using to hold back the water and help turn it back on to defeat Jake and save the town. The hole the three moles dug in the middle of the street? Used to let a blast of water up to blast Jake skyhigh. The rest of the mole's family? Used in a Gondor Calls for Aid to defeat Jake. The one bullet Jake leaves in Rango's gun? Used to free Rango and Bean from the mayor's Death Trap. The crowner is Rango is actually Genre Savvy enough to use it intentionally!
My Little Pony: Friendship Is Magic. There's one for every other episode, and one that was built up over an entire season to boot. The letters Twilight writes to Celestia throughout the first season are used to snap her out of a 10-Minute Retirement and inspire her to fight for her friends and snap them out of Discord's brainwashing.
Season 4 gives us: A top-secret box of mystery, a Pony of Shadows, a magic comic book, and a hint that Fluttershy may still be a vampire. The trinkets obtained by each of the Mane Six over the course of the season are revealed during the finale to be the keys to the mystery box, the comic book is traded by Spike in "Trade Ya!", and it is implied that the Pony of Shadows was Tirek in his weakened state. Whether "Flutterbat" will return remains to be seen.