Did you guys notice that Marvin Berry called his cousin "Chuck" (Chuck Berry?) when Marty was performing "Johnny B. Goode" on stage?
"Chuck! Chuck it's your cousin... your cousin MARVIN BERRY... you know them new sounds you been lookin for? Well listen to THIS!" - Then Marvin holds the phone up to the stage.
There are hundreds of little things in that movie, and each time I watch it, I spot another one of them.