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Batman has so many of these, he gets his own page.
In a Swedish comic book series for children called "Bamse", there is an character who's a turtle called "Skalman" which translates to "Shellman", he can fit anything except for a few exceptionsnote The usual phrase is "Everything except trains, space rockets and Atlantic ferries." into his shell. Think "Deus ex Machina armory".
Grant Morrison, during his run on JLA, introduced Prometheus, a deliberately designed anti-Batman who decided to destroy "the forces of justice" after watching a cop gun down his bank-robber parents. In addition to possessing a helmet that allows him to hardwire his brain to duplicate everything another person knows, including how they move and speak, allowing him to defeat Batman in hand-to-hand combat, he also has plans worked out to disable every single member of the JLA, including the ones who just joined in the previous issue. He is only vanquished when he fails to predict that Catwoman would have snuck onboard the Watchtower to rob the trophy room. Since he didn't plan for her, she takes him out with a surprise whip crack to the soft bits. He has since undergone varying levels of Badass Decay in later appearances.
In JLA: Year One, Martian Manhunter had files on every superhero he knew of, including weaknesses and secret identities. They were again swiped and used by the bad guys.
The Punisher demonstrates this all the time, for several reasons. One, he's a ex-Marine combat veteran who knows the importance of always being ready and having a back-up plan. Second, he's knows he's pretty much always going to be outnumbered and outgunned, so he plans out each mission well in advance, and actively hates other so-called vigilantes who don't plan properly, thereby endangering innocents. In one story, he walked into a birthday party for a mob boss and gunned the man down, leaving immediately thereafter. As he exits the building, he's mentally counting down how long it will take for the shock to wear off, tempers to flare, and for guns to be drawn. At the exact moment he thinks "here they come", a whole pack of mooks bursts through the door after him - to find themselves in the kill zone for the M-60 he was emptying into them, having pre-positioned it earlier.
In another storyline, a group of Special Operations soldiers who'd been sent after him by some corrupt Generals expressed open admiration for his tactics and methodical planning. Frank let the soldiers live but killed all the Generals.
Lampshaded so much in every battle forum he's been, to the point that the comic book community would call him prep god or the #1 prepster in DC (Arguable rivals those of Batman's and Lex Luthor).
Constantine: I heard a joke about you once, E. Mr E: A joke? Constantine: I think it was a joke. Bloke I met in a bar in Kathmandu. Said you always carried a pocket full of stakes, in case you meet a vampire; and a gun loaded with silver bullets, in case you ever met a werewolf. (E pulls a stake out of his Badass Longcoat) Constantine: Blimey.
Professor X had at one point plans to be put into play in the event that any given X-Man executed a Face-Heel Turn. For example, the plan for dealing with Wolverine — immolating his body, severing his head with a laser and sealing it in an adamantium safe.
A word of caution before using this procedure: it will just make him angry.
He's even Genre Savvy enough to know that he isn't immune to being used by villains whose Mind Fu Is Stronger — the first entry in the "Xavier Protocols" is how to take him down. His Genre Savvy-ness also extended to include specific people be required to activate each protocol, so that no one person could access it. Unfortunately, he wasn't quite Genre Savvy enough, since the computer itself went evil...
Grant Morrison has suggested that as part of that protocol Xavier is armed at all times with a high caliber handgun just so he can shoot himself in the head should he ever lose control of his mind.
As revealed in Wolverine, Cyclops apparently has his own set of such protocols. Apparently he has multiple plans for each member, although the only one shown so far are the ones for Wolverine.
Knights of the Dinner Table, a comic about Tabletop Games players / characters, features an extremely cunning player, Brian: When the party is kidnapped and stripped of possessions, he reveals that his character had had "spellbooks" tattooed on the other characters' backs. Not only that, every morning he swallowed a ring of teleportation and every evening he "recovered" it. "It's all there on the character sheet!" Although most of his preparations were on a signed, dated and notarized sheet inside a sealed envelope, so the GM couldn't accuse him of making it up on the fly.
In case he gets his hands on a Wish Spell, Brian also has a pages-long carefully written run-on sentence in his briefcase which is designed to grant his character true immortality. He has even had the document reviewed by an actual paralegal. BA and his fellow Gamemasters cannot find a flaw in the wish, but Brian's PC becoming immortal means that a previously restrained god has the right to destroy him. EVEN THEN this only triggers a clause that undoes the effects of the wish and gives Brian 25,000 gp.
Brian's mage at one point had a custom-made magic helmet that was enchanted to be invisible and designed to project a constant illusion on the inner visor of what the wearer would normally be seeing if not for the helmet being in place. Aside from acting like a magic VR heads-up display, this means that the character is immune to all gaze attacks because he is not technically making eye contact with the attacker. This came up when the party was ambushed by a medusa and seemed to work until B.A. thought to ask how Brian's character could see the illusionary image if the helmet were invisible. Cue Flipping the Table.
Brian also plays characters that are relatives of each other, and Brian has concocted a carefully documented series of contingencies to insure that each succeeding character gets the carefully detailed journals of all his predecessors. The result? Brian's current character always knows everything all of his previous characters knew.
In The Incredible Hulk #375, Rick Jones is caught on an exploding Skrull spaceship. He manages to escape because he has on a parachute, which — as he explains to a boggled Bruce Banner — he carries around just in case he's ever on an exploding Skrull spaceship. It could have been a Shout-Out to Golden Age Captain America, who happened to have a parachute every time it was convenient, with little or no explanation.
Norman Osborn of Spider-Man. According to Mac Gargan he has rooms filled with plans and counterplans. Interestingly enough, Peter Parker himself mentions in one installment that he's pre-planned any fight with any superhero, just in case they go rogue, and also claims that they all do it. Apparently, it didn't work too well when fighting Captain America. That's because Captain America's specialties lie... elsewhere.
In one issue of Impulse, the title character attempted to become Crazy-Prepared by obsessively writing up plans for every conceivable scenario. Despite carrying around reams of paper and Max trying to tell him that he can't possibly plan for every contingency, the plans do wind up saving him when he's attacked by a helicopter — by clogging up its intakes while he furiously searched for his plan on defending himself from a helicopter. This is incredibly funny when you realize that not only did Impulse almost never plan ahead... neither did the writers of the book. Their method of writing the Impulse comic was "we'll make it up as we go along"... and it worked. And is probably the only sane way to write Impulse.
In New Avengers, he whips out some shiny new energy claws to deliver a No-Holds-Barred Beatdown to Namor after he goes against the wishes of the team and blows up a populated world. Presumably he had this tech installed just in case he ever needed to beat the shit out of a Flying Brick.
In Watchmen, Nite Owl has at least three different suits including an underwater owl suit, a radioactive suit, and a snow suit. He also had a couple of spare identities just in case something happens to him for several years.
On the villainy side of things, Lex Luthor does plenty of work to keep himself safe from Superman, but these tend to come back and bite him. He at one point carried a kryptonite ring around on his person at all times just in case Superman would attack, but the radiation from the ring wound up giving him cancer. Another protection he had set up was lining all his buildings in lead to keep Superman from looking into any with his X-Ray vision. When one of the buildings collapsed while he was trapped inside, Superman couldn't find him to bring medical aid.
Comic strip example: When Dilbert's boss uses a ray on him that makes a unicorn horn grow out of his head, the Garbageman offers to fix Dilbert with his cell normalizer and a sample of Dilbert's "pre-unicorn" DNA. When Dilbert asks why the Garbageman has a sample of his DNA, he replies "It's for exactly this kind of situation".
While not at the same level of crazy as Batman, Green Arrow definitely counts. The guy's got a trick arrow for any situation: boxing glove arrows, fire extinguisher arrows, net arrows, geiger counter arrows...
In Gold Digger by Fred Perry, archmage Theodore Diggers faces off against his father, who has become an evil undead abomination. He dodges one of his father's spells by teleporting behind him, where he's most vulnerable. Unfortunately he runs into the invisible time-delayed exploding fireball his father had put there just in case. Then again, if you look carefully, you can see him casting it a few panels before he teleports... Lich King is just Genre Savvy. And knows how Theodore thinks.
"Yes! I had a sword built into Envy's dress in case of emergency! THAT'S JUST THE KIND OF GUY I AM!"
Immortal wizard Quinton Zempfester takes this over the top. As in "I planted this tree 100 years ago because I knew I'd probably need it right about now."
In Secret SixDeadshot is speaking to a priest, trying to understand why he has recently felt such strong urges to just kill everybody he sees, and he relates the story of the first time he fought Batman. At the climax he has Batman dead to rights at point-blank range and shoots him the chest, but Batman does not die as planned and then disarms and apprehends Deadshot. The priest then asked how Batman survived the encounter. Did Deadshot miss? Did the bullets bounce off him? No, he explains that the answer is actually scarier than a person who can dodge bullets or withstand gunshots: Batman had foreseen an eventual confrontation between the two of them, gotten to his gear before the fight and replaced his bullets with blanks!
In a reversal, in Batman: Cacophony Deadshot is hired to kill the Joker, when another, new character shows up, and shoots him in the head at point blank range with a Desert Eagle. Once Batman is on the scene, The Commissioner informs him that the only casualty seems to be Deadshot. He mentions that Deadshot's suit has some kind of sealing mechanism they need to figure out how to get off. Cut to the ambulance, where Deadshot is unzipping his bodybag from the inside. Batman then goes to explain how he is extremely impressed with Deadshot's new suit, double plated helmet with blood squibs in case of a head shot, and bite-trigger-activated self sealing mechanism to mask vital signs, all just so he can "play possum" if ever incapacitated.
Remember how Darkseid used the Omega Sanction on Batman? Well, just in case his plan in Final Crisis failed, he would get his final revenge on Earth by sending Batman to the Stone Age and letting him get reincarnated over and over again, building up Omega energy in his body with each cycle. When he finally reaches the present... Earth-Shattering Kaboom. Fortunately, the heroes figured it out and saved the day.
Quantum of Quantum and Woody, being an Expy of Batman complete with all-purpose Utility Belt. As but one example, he can pull an electronics-disrupting bolo, a portable forensics kit, a grappling hook gun, and a pocket Tibetan dictionary out of his costume without hesitation.
German detective Nick Knatterton wears an artificial back-head in case someone wants to shoot him there, and has a fake beard which also contains a parachute, just in case of.
In the Season Eight Buffy the Vampire Slayer comics, Andrew is very knowledgable about what to do if his giant-sized team mate is in combat with a mechanized version of herself.
The Junior Woodchucks of Uncle Scrooge fame have a medal ready for "Speed reading, ancient languages division, subsection Lydian" to award immediately after completing the feat. When asked, they comment that they are ALWAYS prepared.
In All Fall Down, IQ Squared proves to be this, for programming AIQ Squared, an AI version of himself in the event that he ever lost his super-level genius.
Red Hood and the Outlaws: He's one of the Sons of Batman, so obviously Red Hood is going to be this. A confrontation with gangsters in China shows he hides guns in the potted plants just in case he gets held up without weapons.
Arsenal has a detonation device in his quiver, in case it's ever taken from him.
My Little Pony Micro Series Issue #3: Packing away a huge supply of creativity products despite it being a vacation for her pays off for Rarity and her new friends in the end.
The title character of Diabolik could give Batman a run for his money. In one particular occasion we found out he keeps a version of the formula of his perfect plastic masks altered in such a way a mask realized with it will shrink and suffucate the wearer when exposed to intense sunlight, in case he was being forced to give up the formula to someone who lived in a poorly lighted environment, and has a specific code to stealthily tell Eva it's time to take out that formula. We found out because it happened.
Nick Fury has used S.H.I.E.L.D. resources to build a number of hidden bases and safe houses around the world that only he knows about. He keeps files on every super-powered individual on the planet and to combat Secret Invasion used both to find recruits to combat the Skrull invasion. Brought to new heights by the end of Secret Warriors.
This extends to the movies as well. In Captain America: The Winter Soldier, he manages to evade an assassination attempt by injecting himself with a drug that induces a Faux Death state, and then heads off for a secret safe house that only his closest associates know about.
Not to mention the fact that he programed the S.H.I.E.L.D. computer to accept his blind eye's retinal scan just in case his enemies deleted his normal eye retinal scan from the database.
Thanos as well. Writer Jim Starlin introduced the concept of the Thanosi, Expendable Clones that Thanos has just in case of emergencies. These have mostly been used to Retcon away embarrassing defeats or Out of Character moments by saying "Oh, that wasn't the real Thanos who got his ass kicked by D-Man."