Say what? Where am I supposed to find this if I don't want the roll of film?

Great idea by the way. I would go further and make two tiny holes, one in the cap, and one in the bottom, and run a small piece of brass wire through it to be able to suspend it. No, wait, even better : glue a closed zip-tie onto the cap using Loctite so you can just suspend the small canister off a piece of paracord or something.