From Thread Theory:
Sew a wallet that is as minimalist as they come! This elastic wallet can expand to fit up to ten cards within its three elastic pockets but will also snugly carry as little as two cards and some cash. Personalise this wallet with colourful elastic and a contrast cash pocket made from leather, Kraft-tex, Tyvek or felt. Add an optional tag and key ring so the wallet may be attached to keys, a lanyard or secured within a bag.
This wallet is made from 2" (5 cm) wide knitted elastic which is very strong. It is slightly shorter than a standard card so that the cards are accessible yet secure.