SlimFold “MICRO Soft Shell” Wallet
At first glance, the MICRO Soft Shell wallet by SlimFold seems like any other slim, minimal wallet out there: It holds 8–12 cards, some cash, and it's got a little window slot for keeping an ID in. However, the real magic here is in the material. This stuff is super-light, waterproof, stain-resistant, crash-tested up to 70mph, and is even machine-washable, all while being less than 0.5mm thick.
You can get one in a few different colorways for $45 at Amazon.