Dr. Emmett Brown's outlook on life had changed, since he knew that he was going to successfully build a time machine. This new outlook caused Doc to piece together Marty's letter that he stuck in his pocket in 1955. This saved his life in the new 1985, since he knew to wear a bulletproof vest when the Libyans found him.
Marty now owned a Toyota 4x4, that his counterpart saved up for all summer, while his father paid the rest.
Marty's counterpart planned to take his girlfriend Jennifer Parker in his 4x4, instead of in the family car. The rest of the family would still have transportation, as Biff didn't wreck the family's car in this timeline.
Biff now owned Biff's Auto Detailing, as he no longer could bully George into writing reports for jobs in which he wasn't qualified. Biff waxed Marty's truck, along with the family's BMW 733i, so that it would be ready for Marty's date.
Lone Pine Mall, which was created instead of the Twin Pines Mall, due to Marty accidentally running over one of the twin pines at Otis Peabody's ranch with the DeLorean in 1955.
Alternate timeline of events
Saturday, October 26:
Marty arrives back in 1985 early to save Doc, but the car dies and Marty runs down to the Lone Pine Mall.
Marty watches Doc get shot again and his other self travel back in time.
Marty finds that Doc was wearing a bulletproof vest, as a result of reading Marty's letter to him warning of his death.
Sunday, October 27: Douglas J. Needles dared Marty to compete in a drag race by calling him chicken. Needles narrowly missed hitting a Rolls-Royce Silver Cloud I, but Marty crashed right into it, injuring his hand which prevented him from ever playing the guitar again. The accident also financially ruined him, as he had a large debt to pay for the damages to the Rolls Royce.
Behind the scenes
Since Doc didn't live through the timeline from which Marty left, he named the alternate timeline where Biff controlled Hill Valley as "1985A" on a blackboard in his trashed lab. That timeline is actually the second alternate timeline that Marty witnessed, as this is the first.
When Marty discusses this timeline, he describes it as the timeline where he hit the Rolls Royce.