From Thread Theory:
Sew an unobtrusive wallet perfect for the back pocket of jeans. This minimalist design carries only the items you really need: Up to six cards and folded cash will be safely stored within its three pockets. The angled design allows for quick access to your most used cards.
Stitch this wallet up in just a few minutes using fabric, felt, or specialty materials such as leather, Tyvek or Kraft-tex. Separate instructions and pattern pieces are included to suit your material choice. A leather storage pocket can be added to all three options to store a single key or a guitar pick.