Assuming that we're talking about out-of-print master copies, and not one of the many bootlegs that I own, I would save the following:
Hard Knocks: The Chris Benoit Story (DVD)
Somewhere down the line I will be glad that I kept this around.
Starrcade '87: Chi-Town Heat (VHS)
The only NWA master in my colleciton.
AWA All-Star Wrestling (VHS)
Rare as fuck cassette featuring Rick Martel, Jumbo Tsuruta, Michael Hayes, Verne Gagne and Nick Bockwinkel.
I do, however, have binders full of non-commercial footage that are more accessible and easier to grab on the way out, but that's neither here nor there.