Well, by reasonable context anything you can't leave lying around for a couple of decades and expect to work, or stick in a reasonably constant environment and expect to be around in a hundred years. HDDs, optical discs - that sort of thing, I'd consider to tend to be fairly fragile.
Anything that wouldn't be accessible to historians in the same sense that photographic stuff is basically.
Anything that wouldn't be accessible to historians in the same sense that photographic stuff is basically.