Corrected entry: In the scene where Marty is watching his other self talking to his parents (his other self just played Johnny B. Goode), he is watching through the door, when suddenly Biff turns up and they argue. When they are about three feet away from each other (just enough space for a door to be opened) you see Marty blinking his eye, because he expects the door to be slammed open, and the Marty from the first film rushes out.
Corrected entry: This is the part in the very beginning when Doc takes Marty and Jennifer to the future. Wouldn't the future be without Marty and Jennifer because they left in 1985 and must have been missing all that time. From 1985-2015. Thus, there would be no way in heck that they would have existed in 2015, and no way that the 1985 Jennifer would have seen herself or her house, family etc.
Corrected entry: In the scene where Biff gets the sports almanac from "Gramps" Biff in his garage, Gramps gives Biff the sports almanac. Biff looks at it, makes a dumb comment and then gets slapped for it, then tosses it in the backseat. But you'll notice Gramps still has the almanac in his hands and uses the book to show the results of the UCLA game. When Biff is given the book for the second time, it is tossed in the backseat again. (01:08:35)