These aluminum capsules are great for keeping things dry that need to stay dry. Stuff pills, tinder, or anything else inside. These are small and light enough to keep on your keyring and never notice they are there, until you need them. There is an o-ring to make it watertight, and a split ring so you can attach it to your keychain, pack, or anywhere else.
Please note that the pictured battery is not included and is just for size reference.