I found a light alloy tube - originally part of a cigarette lighter that was the size and shape of a cigarette. Made holes in it to take a split ring, then wrapped the duct tape around it.

I am leary of putting stuff in my wallet. I find it quickly gets too thick. For a while I carried a fresnel lens in it, but it was too thick, and duct tape tends to be thicker. A bunch of stuff loose or on a keyring seems to take less room.