If you haven't heard by now it has been revealed that the upcoming Ant-Man (coming July 17th) has two credits scenes attached -- a mid credit scene and a post credit one.
If you want to know the contents of those two credits you can find a Moviepilot article spoiling the contents of those two scenes here. Read it a your own risk.
Without being overly spoilery, the first scene teases a new hero. The second alludes to the upcoming Captain America: Civil War.
In an interview with io9, Marvel President Kevin Feige explained how the post credit scene came to being:
"I was watching Civil War dailies and said, ‘Whoa, that could be the tag.’"
The second credit scene contains an actual scene from Captain America: Civil War. It is essentially a teaser piece.
Civil War is being directed by the Russo Brothers and is schedule for release in May 2016. It is no secret that Ant-Man as well as every other Avenger will be featured in the movie. It is not subtitled Civil War by accident.
Director Peyton Reed originally scripted and almost shot a more comical post-credit scene. Reed acknowledged that the teaser scene would be a perfect closing for Ant-Man and great setup for Civil War.
There has been speculation that Marc Ruffalo would be returning as the Hulk in [Captain America: Civil War](tag:994409). That is based on a rumor that had Robert Downey Jr. relaying that fact to an incredulous Ruffalo.
Feige commented about the rumor to io9:
"[Hulk] is not a primary part of Civil War. He may not be a part at all."