During a lull in the action, Cpl. Hicks takes the time to teach Ripley how to use the Marines' weapons. This allow her to go on her Mama Bear rampage at the end.
Black Widow's introduction in The Avengers has her "interrogating" an arms dealer by making him think he's outsmarted her, has her at his mercy, and is free to monologue, thus revealing information. She later uses this same strategy against Loki when he thinks he's caused her to have a Heroic BSOD.
As she later tells Hawkeye after his recovery, she actually was emotionally compromised but pulled it off anyway, likely a reference to the kind of conditioning/training she overcame to defect from the Russians in the first place. In addition, Loki himself uses a skill from his own past, namely the illusionary images from the Thor movie: "Will you ever not fall for that?"
Back to the Future: Marty holds onto cars while skateboarding in Part I in 1985. He uses the same trick in 1955 to escape Biff's gang on a plank with wheels, then on a hoverboard in Part 2 to steal the Almanac from Biff, and then to travel along a train in Part 3.
In Bandits, Harvey is learning special effects when Joe and Terry first meet him. They will become handy in the last scene.
In Big Trouble in Little China, Jack catches a bottle as it hurtles toward his face. Later he displays the same skill by catching a knife thrown at him. After both feats, he casually says, "All in the reflexes."
In Birthday Girl, the protagonist is shown rigorously jogging every morning. Later, he is able to catch up to a slow-moving car.
Surprisingly averted in The Brothers Bloom, in which Penelope Stamp is a "collector of hobbies" and has an untold number of skills revealed in a humorous montage. None of these skills actually come to help her in any way.
in Conspiracy Theory, Jerry regurlarly observes Alive in her apartment training on an stepper exercising machine. Later, when they get attacked by CIA goons, Jonas gloats that they will get her, but Jerry knows better and tells him "you've never seen her run", and she indeed escapes the scene.
In Cowboys and Aliens, Meacham spends time teaching "Doc" how to shoot a rifle. Later, Doc uses that rifle to pick off an alien that's about to take down Colonel Dolarhyde.
In Death Proof, it's established early on that two of the four heroines are stunt drivers, just like Stuntman Mike, which comes in handy during the car chase.
Planet Terror lampshades the trope, with Cherry listing off a number of her many "useless talents", all of which become quite useful during the final gunfight.
Subverted in Demolition Man. Much is made of Spartan's implanted knitting skills, but the most that comes of it is when he makes Huxley a sweater by way of apology.
It may not be a proper example of the trope, as it's really just a way to get them to ask the question "If that was Spartan's rehab program, what was Simon Phoenix's?"
Another near-miss of the trope in the movie would be Huxley's skill at martial arts: While she has a perfectly wild explanation for them ("Jackie Chan movies!"), she's not actually shown watching any. Had she been, the later ass-kicking would have played into the trope perfectly.
In Dragonheart: A New Beginning, Drake attempts to learn the lost dragon art of breathing ice. He never quite gets it down, but manages to pull it off in the climax of the final battle.
Executive Decision: In his very first scene, David Grant lands a small airplane during a flying lesson. He is very nervous about his first solo flight and remarks, "God, why am I doing this?" At the end of the film, both pilots of the hijacked 747 are shot dead and David must land the plane.
Face/Off combines this with Chekhov's Gun when the villain (who thanks to a surgical face swap is posing as the hero) gives a knife to the hero's daughter and teaches her a technique for stabbing someone. Later, after he's shown his True Colors and is now threatening her, she pulls out the knife he gave her and stabs him the way he taught her.
One Flintstones movie subverts it has Fred bowl a perfect game at the beginning. Then later own the villain has kidnapped Wilma and is standing on a bridge over a volcano, Fred picks up a round rock and bowls it at him completely misses.
In Galaxy Quest, Jason Nesmith decides to try doing his signature "forward-roll" maneuver (that he hadn't done since the show ended) when the crew first lands on the rock planet. Gwen DeMarco asks Nesmith why he's doing it, and Nesmith remarks that he hasn't done it in many years and wanted to try it out. It comes in handy during the second-last scene where, after Sarris emerges from the wreckage of the ship, Nesmith grabs Tommy Webber's gun before using the forward-roll maneuver and gets in place to shoot him.
The Heat: Mullins' groin Russian Roulette on a perp ends up being a subversion: she never had bullets in the gun...which Ashburn only learns after actually shooting a guy in the crotch.
Subverted also by the emergency tracheotomy, which ends up doing more harm than good.
Averted in Honeymoon In Vegas. Although Nicholas Cage's character is a private investigator, this fact plays no part in his efforts to locate his fiancée.
The Host has Nam-joo, an archer who tends to hesitate too much. Obviously, both parts of this come into play by the end of the film.
In Hostel, it's established in early scenes that Paxton speaks German. Later on, he uses it to plead for his life to his German torturer. It doesn't help much — he just ends up with a gag in his mouth as a result — but the torturer is visibly rattled by it.
In Hot Rod, Rod learns a Tai Chi move that makes the target lose control of their bowels from Denise. In the ending, he uses this technique on his stepfather as a finishing move.
Julia Roberts' character in I Love Trouble (an eminently forgettable film) can palm small objects like coins. This comes in handy at the end of the movie.
Early on in I Robot, Sonny notices Detective Spooner winking at his chief, who then explains that it's a sign of reassurance. Later on, Sonny takes Dr. Calvin hostage after learning about VIKI's plan and threatens Spooner before giving him a wink.
In Iron Man 1, Tony Stark is testing his Mk. II armor's flight capabilities, and decides to break the altitude record, just because. He fails because the suit builds up a layer of ice which shorts out its systems; Tony later Hand Waves a fix for this. Later in the movie, he lures the Big Bad Iron Monger to similar altitudes, causing Iron Monger's suit to freeze up while his own suit is protected.
In Iron Man 2, a similar thing happens during the fight at his birthday, Tony and Rhodey connect repulsor blasts and cause an explosion, they later use the same technique to defeat Whiplash.
Another, more villainous example is Ivan's computer hacking skills.
Natasha Romanoff's martial arts skills also come in handy.
The Karate Kid: Paint the fence, paint the house, Wax On, Wax Off... Danny Laruso tended to use a new Chekhov's Skill as the main means of defeating opponents at the end of a movie. He tended to get his ass kicked across the screen for the remainder of all three movies. Each film featured a Chekhovs Skill, the most famous one being the Crane Kick. When the crane kick failed in the second movie, Daniel had to turn to the drum technique. The third movie had Daniel psych out his opponent his kata moves he learned, and in the fourth movie Julie used the praying mantis kick. The remake has Drey mimic the woman who was controlling the cobra with extreme concentration.
Also from the fourth movie: Julie learning how to fight blindfolded. It comes in handy when she cops A Handful for an Eye.
In Kill Bill Volume II, we learn in flashback that the Bride's amazing skills were taught to her by Pai Mei. This is effectively demonstrated in the Texas Funeral sequence (in which the utility of the one-inch punch triggered the flashback in the first place - also a Shout Out to Bruce Lee). Then she uses the eye-pluck to permanently disable Elle Driver (foreshadowed thrice: a Crazy 88 henchman in Vol. I, Bill mentions it when he delivers her to Pai Mei, then Elle herself, in flashback, suffers it). Later, during the final duel with Bill, we finally see the Bride use Pai Mei's final secret, that he taught no one else: the Five Point Palm Exploding Heart Technique.
In Knight and Day, Tom Cruise gives Cameron Diaz a patient onscreen lesson on how to break free when an attacker grabs you from behind. She needs that skill a ridiculously short time later.
Quatermain, in The League of Extraordinary Gentlemen, spends a very Dramatic Scene teaching impudent Tom Sawyer how to shoot his elephant gun, counseling him on taking his time and feeling the shot. This is vitally important at the climax, when this skill is needed to take down the escaping Big Bad.
Lethal Weapon 2. Riggs wins a bet early in the movie by getting out of a straitjacket because he can dislocate his shoulder. This comes in handy when he is thrown in the ocean in a straitjacket.
Similarly, in The Lovely Bones, Lindsey's regular jogging allows her to outrun and escape Harvey.
The Korean film "The Man from Nowhere" builds the plot around an anti-social pawn shop owner who is an ex-Special Forces member who was presumed dead, which explains how he manages to beat the crap out of everyone in the movie.
The original The Man Who Knew Too Much does it with guns.
Marathon Man. Dustin Hoffman character's training as a marathon runner comes in handy when he escapes from ex-Nazi Szell and outruns his henchmen.
In Master and Commander Stephen Maturin's interest in science is a constant thorn in Jack Aubrey's side; right up until one of his zoo specimen's gives him the necessary strategy to take down the enemy ship.
It's established early on in the third Mission: Impossible film that Ethan can read lips; one of his superiors later has to silently mouth orders to him, so as not to arouse suspicion from a mole in IMF. Also, Ethan's wife is a nurse; the climax of the film has Ethan stopping his heart with an improvised defibrilator, his wife revives him with CPR.
Mystery Men: It's a Running Gag throughout the film that Invisible Boy can only turn invisible when there are no people watching. Consequently, we never get to see him use his power; he is merely told "your time will come". In the climactic assault on Big Bad Casanova Frankenstein's lair, Invisible Boy is able to turn invisible in front of a camera-operated laser and thus circumvent it.
Flint is shown putting himself in suspended animation and later waking himself up when his watch alarm goes off. He later uses this ability to put himself in suspended animation and appear to be dead so Galaxy will take him to its Island Base.
Flint is shown fencing with several men and defeating them. Late in the movie he fences with Rodney.
In Outlander, Wulfren challenges Kainen to a friendly contest of shield-jumping, and Kainen turns out to be the first person to match Wulfren's skill. Kainen later volunteers himself and Wulfren to serve as bait to trap a monster: they use shields atop posts as stepping-stones over the pit, and when the monster tries to follow, it falls in.
In The Curse of the Black Pearl, Will Turner demonstrates his skill at throwing swords in his fight with Jack Sparrow at the beginning. This skill ends up saving Jack's life during the climax, as Will throws his sword to prevent Jack from falling too far when he is hanged.
Also, in On Stranger Tides, while you might not notice it when watching it for the first time, Scrum plays and sings "My Jolly Sailor Bold" at the Captain's Daughter. Later, he has to sing that song in order to attract mermaids.
Elizabeth's childhood obsession with pirates comes in handy a few times:
In The Curse of the Black Pearl, her knowledge of the Pirate Code allows her to negotiate a Parley with Barbossa and her knowledge of piracy and sailing in general inspires her last-second stunt while the Interceptor is being pursued by the Pearl.
In At World's End she becomes a Pirate Lord, and then Pirate King. She also inspires the troops with a speech about the power of piracy.
Jack escapes from the Dutchman's jail in At World's End using the same trick that Will used in the first film to free him.
In Small Time Crooks, several characters comment on Frenchy's cookies before she sets up the shop and becomes successful.
In Star Wars A New Hope, Obi-Wan began teaching Luke about how to sense things out with the force and not rely on sight. This was used in a lightsaber training exercise, but a voice from beyond Obi-Wan gives Luke the same advice when it came to making the Million to One Chance of hitting the Death Star's Achilles' Heel, instead of relying on targeting computers that had failed another pilot before.
Tenacious D in The Pick of Destiny is filled with these. The boys use their power slide to get through a closing security door and the infamous cock push-up to press a security button. While evading the police, KG uses his video game driving skills, though this point was mostly left on the cutting room floor. They use the power of their rocking to save themselves from Satan.
In the South African comedy There's a Zulu On My Stoep (AKA Yankee Zulu), Zulu Mashebela was known as "the champion mud slinger of the world", able to throw mud (or anything mud-like) from a stick with deadly accuracy. In the end, this is not only used to defeat the Big Bad but also to reveal to his daughter that he is her father, who only knew this one fact about him.
In Thor, Jane Foster's area of research is the creation of an Einstein-Rosen Bridge. After the Bifrost Bridge was destroyed, Jane attempts to create a bridge from Earth in order to reach Asgard.
Also Loki's ability to create illusionary duplicates of himself. And his knowledge of pathways between the worlds other than the Bifrost.
In Titanic, Jack teaches Rose how to "spit like a man," and she later uses it to get away from Cal when she distracts him by spitting in his eye
Early in the 2008 horror film, Train, when the protagonist is having doubts about her future in wrestling, her boyfriend, who's on the men's team, teaches her a move he calls the "Todd Patterson invincible double leg double hook throw". In the end, she uses this move to take out the last antagonist.
During the start of TRON Legacy, Sam displays athleticism as he was evading Encom security and the police, which he would need to survive the games.
Sam's motorcycle skills comes in handy when he is in the light cycle games. His BASE-jumping skills, shown as he escapes from the Encom tower, helps him and Quorra escape from Clu's quarters. Sam even lampshades this to Kevin.
In the Serbian film Underground, we learn that the electrician Blacky is completely immune to electric shocks. He can bite a live wire with no discomfort at all. Later, he easily resists Nazi Electric Torture to the point that a confused Nazi captor incapacitates himself trying to test the equipment for malfunction.
Under Siege 2 Dark Territory. Bobby Zach is taken out with a judo move used on him by Sarah Ryback (humorously). He is soon after shown practicing the move on himself. He finally puts it to some use when he throws skilled mercenary Afifi from a helicopter with the same move.
Emily's flag-twirling in White House Down. She uses her flag-twirling skills to wave off the air strike using the presidential flag.
Mariko mentions in passing that as a teen, she was a champion knife-thrower. In the finale, she deals a critical blow to the Silver Samurai by hurling one of Logan's severed claws into the villain's skull.
Used straight and then inverted in Yes-Man. Carl learns to play guitar, speak Korean, and fly a plane. The ability to speak Korean and play guitar are used to his advantage...but the plane lessons and Korean get him targeted by Homeland Security.
In Zoolander, Derek Zoolander is obsessed with perfecting his new "Magnum" expression. Later, in the climax, he uses it to stop a shuriken aimed at the Prime Minister of Malaysia, halting the projectile in midair.