This is a bit of a prototype. I picked up some keyring hoops with the intention of attaching Scottish agates to them. It turns out I don't have the machinery for putting holes in agates, but I do have hagstones. So now you can carry good luck with you, wherever you go.
Scottish hagstones were traditionally used to keep evil witches, or hags, away. They are considered fey spotting stones. Full disclosure: I have yet to spot any through the stone.