The Marvel Cinematic Universe completely changed the superhero genre when it was first introduced and has continued to do so throughout the years. One major way they changed blockbusters was by popularizing post-credit scenes that would play after the movie was over, giving fans an extra scene or two before having to leave the theatre.
Since the franchise was just finding its footing in phase 1, the majority of the post-credit scenes were used to hint at the introduction of the main heroes and tease the Avengers becoming a team.
The Incredible Hulk
The Incredible Hulk's post-credit scene shows after the Hulk and Abomination fight that took place in Harlem. Soon Tony Stark enters the bar and after the two exchange a few quips with each other, he then tells Ross that they're putting together a team and when Ross asks who else he's referring to, he smiles before it cuts to black. While this moment isn't directly referenced again, it was intended to hint at Bruce Banner being considered for a spot on the Avengers. Considering this scene had no real importance since all it did was nod at the possibility of Hulk ing the team without really setting anything up, it is easily the weakest out of them all.
Captain America: The First Avenger
The post-credit scene of recently revived Steve Rogers in Fogwell's Gym, laying into a punching bag before knocking it off the hook and across the room, causing it to burst.
A few seconds later, he is approached by SHIELD director Nick Fury with a mission for him. Steve asks if Fury is trying to get him back into the world and Fury responds that he's trying to save it. The scene then transitions into a full teaser trailer, setting up the events of the team-up movie. Even though the Avengers trailer was a great added bonus, the fact that the scene was just a shorter version of a better scene that was coming in the next movie made it less worth it.
Iron Man 2
The post-credit scene of Thor has his powers revoked and his hammer is thrown down to Earth, making this the first big-screen appearance of Mjolnir in the MCU.
Thor
The post-credit scene of Thor shows Erik Selvig meeting with Nick Fury after the events of New Mexico. After the two talk for a while, Fury shows him the tesseract and says that it could be a source of unlimited power if they figure out how to tap into it. While Selvig looks at the cube, Loki can be seen walking up next to him in the reflection of a nearby mirror while still being unseen by Fury and Selvig himself before whispering "Well, I guess that's worth a look" which Selvig then repeats back to Fury. Not only did this moment reveal that the God of Mischief managed to survive his dramatic fall from the Rainbow Bridge, but it also set up his role as the main villain of The Avengers and the control he would have over Selvig's mind.
The Avengers
After almost sacrificing himself by sending a missile through a wormhole and being woken up by Hulk, Tony suggests that the team go and get Shawarma after the battle since none of them had tried it. It seemed like a throwaway line during the movie but the movie's second post-credit scene shows that Tony was being completely serious.
It shows all six Avengers sitting down in a ransacked Shawarma restaurant after the battle, eating silently while the workers try to clean up debris in the background. Despite not really serving a purpose in the story beyond providing fans with an added moment, this is easily one of the most iconic out of all the post-credit scenes from, not only phase 1 but the entire MCU.
Iron Man
The post-credit scene of introducing himself as Nick Fury, Director of SHIELD, and saying he's there to talk to him about the Avenger Initiative. While comic fans immediately knew what he meant, this was the audience's first hint that there were more superpowered characters out there and that they would eventually forces, although it wouldn't happen for another 4 years.
The Avengers
The first post-credit scene opens with Thanos' advisor, The Other, telling him that the humans are not what they expected and that challenging them is to "court death" before Thanos turns to him and grins. While his reasoning for wanting the stones was later changed, the line was a nice nod to Thanos' original motivation from the comics of him wanting to attract the attention of Lady Death. Also, despite the fact that Loki was working on his behalf for most of the movie, this was the first real appearance of the Mad Titan in the MCU which got plenty of fans excited for his future appearances.
