Ladies and Gentlemen, allow me to reccomend the Big Skinny wallet, billed as the "world's thinnest wallet."
http://www.bigskinny.net/super-skinny-tuxedo-black.html

(They have many styles of wallets, but the one I linked to is the one I own).

I have, for years, used a fairly typical men's tri-fold leather wallet. It was wearing out. I saw an ad for this company. Was kind of skeptical about their claims for it being so thin, but decided since I needed a new wallet anyway, I'd try it out.

I have been EXTREMELY happy with this purchase. I'm able to hold everything in this wallet that I had been in my old one, but it's easily only about a quarter the thickness. It fits easily in all my sporrans, in terms of it's length and width, but because it is so incredibly thin, it takes up next to no actual space in my sporran, leaving plenty of room for keys, cell phone, chap stick, etc.

I've reccomended it to many people since I received mine. I've had it for a number of months now, and am still very pleased with this purchase.

M