PROLOUGE
One morning in Hill Valley, Marty MCfly was getting ready for school; the phone rang and doc. called him to the railroad crossing at 2:00 AM tomorrow. That very second a blast of light threatened Marty as the time train whizzed out of the time continuem. The wing doors opened, there revealed Doc. Emmet Brown. Who called him in to the time train, Doc. Sat in the driver's seat and hovered to 88 MPH thus taking them into 2102.
"We came here to make history by taking notes far ahead of present time!" They landed on a nearby railroad track and they climbed out. "Where are Clara and the boys?" said Marty. They didn't want to get killed from destroying the space-time continuem. They walked into town and got some cheese-burgers for lunch.
This is only the prologue so don't get all fussy about it.