Not necessarily unique, but I mostly always carry a small pouch containing a full D&D dice set.
I haven't needed dice in... years, now that I think about it, but I carry them as a symbol of luck. Not good luck or bad luck, just luck, chance. Helps me keep things in perspective when everything goes sideways.
As I've said, a symbol of luck, not necessarily of good luck. A sort of Memento Mori, but for the fact that no matter how hard you try, sometimes it's just not up to you.
Ah, but you see, I'm not looking for a good luck thing! Having the one which always works against my best interests is a reminder that everything is about balance! Some are lucky, some are unlucky, and that's just how life goes!