Start slammin' cold ones this summer cuz bottle caps are the raw ingredient for this round of homebrew geocoins. Throw some bling-bling glitter and custom logos in the bottom of a bottle cap, then fill it with two cc's of epoxy, and cha-ching! instant personalized geocoin. Photos, bugs, sprinkles, candy, and wire are the sorts of mixed media that can be cast into the epoxy. Try googling "bottle cap art" to get more ideas and have fun collecting those caps. Extra tip: You can probably pick up a free 6CC syringe at your local pharmacy if you don't look like a heroin addict (sorry ma).
Bottle Cap: $0.03
Mixed Media: $0.01