Just before their first encounter with the Brain Trust, Achilles of the Global Guardians teaches his teammate Arachne how to use a pick to open a set of handcuffs while her hands are cuffed behind her back. By the end of the story, she's used this brand new skill twice.
This sometimes happens in Survival of the Fittest with the profiles of the characters. Newbies often try to cram in as many potentially useful skills as possible (such as survival training, firearm proficiency and martial arts. Made ridiculous when you consider that the characters are supposed to be Ordinary High School Students
In Yu-Gi-Oh! The Abridged Series, Kimo (the guy who always talks about his hair) mentions taking child grabbing classes. It comes in handy several times.
Kimo: Attention duelists! Those child grabbing classes were worth every penny!
In Doom House, Reginald P. Linux's ability to throw the doll, first demonstrated when he's trying to remove the doll from his new house, comes in handy later when he must fight the terrorist.
The Autobiography of Jane Eyre: It's established in the first episode that Jane is a nurse, but she's pursuing a new degree and becomes a tutor. She also showed her competence when Mr Rochester had a minor car accident and sprained his ankle. Her nursing ability came really handy later in episode 13 "Crash" when Mr Rochester was mysteriously injured and was bleeding quite a lot. Jane fixed his arm real nice.
During their altercation in a flashback sequence in Episode 2 of Nightwing: The Series, Dick attempts to slug Bruce in the face, only for Bruce to block the attack and use a spinning counterattack that stops just short of Dick's neck; Bruce does this to prove his point that Dick's not yet ready to go solo. Nightwing later uses the exact same maneuver to win his rematch with Deathstroke in Episode 5.