20 Things You Somehow Missed In Back To The Future Part 2
17. Doc's Shirt Foreshadows The Events Of Part III
Early on in the movie, we see that Doc is wearing a shirt with a white, blue, and yellow patterned design on it, though you couldn't be blamed for failing to notice what it is or its future significance.
The shirt actually depicts cowboys on horseback chasing a train, which is very clearly foreshadowing the events of the western-themed third film, where both horses and trains play a major part in the narrative.
But the gag doesn't just end there: in Back to the Future Part III, Doc actually uses this shirt as a bandana while performing a stickup, though the material's design can only barely be made out through the reversed fabric covering Doc's face.
Clearly, one of the major benefits of shooting two sequels back-to-back is the ability to include ingenious foreshadowing like this.