In Back to the Future, Part II, Marty McFly watches promotional footage for the Biff Tannen Museum in a dystopian 1985. A rare VHS copy of this ad was recently unearthed, so make like a tree and check it out.
Says the footage-finder at BTTF.com:
The 3½ minute segment was digitized from an old VHS tape which had been saved by a Back to the Future fan with family connections to the film production at the time the sequels were shot in 1989-1990. To date, the following clip is not available on any other commercial collection, including the recently released 25th Anniversary Trilogy Blu-ray Disc and DVD boxed sets.