In Back to the Future, the original idea was for the time machine to be a refrigerator, but because Robert Zemeckis was afraid that kids would imitate the film and get trapped in fridges, they changed it to a DeLorean car.
The DeLorean in Back to the Future used a custom built speedometer that went up to 95mph. The normal speedometer only went up to 85mph due to a 1979 mandate signed by Jimmy Carter.
Back to the Future was rejected by Disney they said a mother falling in love with her son is not appropriate for a family film.
When Ronald Reagan watched Back to the Future for the first time, he loved the joke about who was president in 1985 (Ronald Reagan? The Actor?) so much that he made the theater projectionist stop the film, roll it back, and play the joke again.
Back to The Future Part II correctly predicted the widespread use of wall mounted flat screen TVs, routine plastic surgery, handheld computer devices, hands free gaming, and the popularity of 3D movies in 2015.