Let's see...
1) As WalterM mentioned, I use a few for the "spare" parts from various laptop computers I've worked on and/or cannibalized for various clients.
2) I use them to "B-wind" color-neg rolls I get from the lab (pro or mini), always uncut, in order to eliminate or minimize curl. (This is less of a problem with Kodak's top-tier films, but still a bit of an issue with stuff like their Gold color-neg films.)
3) One film container will hold one set of spare CR-2 batteries for one of my Hexar RF bodies, and one CR-123A battery for my Contax Tvs. Since the "lease" on my Leica M2 is about up (and the owner hasn't offered an option to buy), having spare batteries on hand is a slightly bigger deal, although the Hex and Contax are fairly miserly in terms of energy consumption.
4) Great for keeping earplugs on hand when riding the subway!
- Barrett