Charlie (Nicolas Cage) begs Peggy to marry him, saying he doesn't know what the future might bring; he might lose his arm, even. In Cage's next film, Moonstruck (1987), he played a baker who has lost his hand.
In the original script, Rosalie, the woman in the wheelchair at Peggy Sue's high school reunion, was a gymnast who was crippled in an accident. In the original script, Peggy Sue tried to take advantage of her knowledge of the future. She invented pantyhose, encouraged people to invest in Xerox, and tried to prevent Rosalie from hurting herself.
While "visiting" 1960, Peggy Sue warns her sister about eating red M&Ms. Red M&Ms were discontinued in 1976, when Red #2 dye was found to cause cancer. They were reintroduced in 1986, soon after the film was released, with a different red dye.
The opening shot of the film is an optical illusion. Because the camera and crew would have been seen in the reflection of the mirror had the scene been shot in a conventional manner, there is a body double for Turner (only she can be seen from behind in the shot) on the other side of the "mirror", doing the exact opposite of the star's movements, giving the illusion that Turner and Hunt are reflections, when in fact they are the real actors in tableau with a body double sitting in front of them with her back to the camera in front of an empty mirror frame, framing a hole in the wall of the set.
Kathleen Turner usually feels the role she's playing intensely. In this movie she had terrible nightmares about her dead grandmother calling her on the phone, similar to what Peggy Sue feels in the phone scene.