I use the All-Ett (http://www.all-ett.com/) which bills itself as the world’s thinnest wallet. It’s made of nylon sailcloth. It feels wierd, and looks ugly, but it is so much thinner than anything else I’ve ever used that it’s worth it. I used to take out my wallet when I sat down, which led to difficulty several times. Now, I hardly even know the wallet’s there. (I know, I sound like a commercial, or a raving fanboy).

The thin material, and the four non-overlapping pockets, and the lack of other junk (like windows for licenses, etc) really allow me to carry all the stuff I need, but still stay slim…