The day before filming a fight scene with Robert Downey Jr., Sebastian Stan sent him a video of himself doing intense bicep curls in front of the decapitated head of an Iron Man suit. He attached the message, "Looking forward to our scene tomorrow Robert."
Sebastian Stan revealed that the backpack that Bucky is seen wearing in the trailers contains journals that he has put together of his scattered memories.
Tom Hiddleston confessed that even though he did not appear in the film, it contained one of his favorite moments in the Marvel Cinematic Universe, the helicopter scene. He enthused, "I mean Chris Evans does a bicep curl, with a helicopter! If you don't love that, we can't be friends."
T'Challa had a much smaller role in the earlier drafts and did not even appear in costume, as the writers intended to put more focus on Spider-Man, and save Black Panther's origin for his own movie. However, when it looked like Marvel would not be getting permission to use Spider-Man, Black Panther's role was beefed up significantly. By the time they did get to use Spider-Man, T'Challa had already become so integral to the plot that they decided to leave his role as it was, and give Spider-Man a smaller part.
No CGI was used during the highway chase scene when Bucky commandeers a moving motorcycle from under its rider. The whole stunt was practical.
Alfre Woodard: (at around 17 mins) as Miriam Sharpe, the mother of an American citizen killed in the battle of Sokovia. Woodard was suggested for the role by Robert Downey Jr. before Marvel Studios learned of her casting as Mariah Dillard in Luke Cage (2016).
Ann Russo: The wife of co-director Anthony Russo provided the voice of Helmut Zemo's wife in the message box of Zemo's phone.
Jim Rash: (at around 16 mins) As the MIT liaison. The Russo brothers previously worked with Rash on Community (2009).
Stan Lee: Stan Lee's second cameo playing a delivery man. In this movie, he played a FedEx driver delivering a package to Tony Stark (Robert Downey Jr.). In Fantastic Four (2005), he played Willie Lumpkin, a USPS mailman who delivered Reed Richards's (Ioan Gruffudd) mail to him early in the movie.