Among the many varieties of wallet/iPhone cases is Distil Union’s Wally. It’s an attachable leather pocket that keeps your credit cards close at hand, with a pull-tab that conceals/reveals contents. It won’t hold all your George Costanza-like receipts and such, as there’s just room for around 3 cards, so maybe it will force you to only keep what’s necessary. The Wally attaches directly to the iPhone (and most cases) with an adhesive backing.
-Accommodates the 3 cards you carry most
-Securely attaches directly to iPhone and most cases
-Pull-tab action conceals and reveals your contents
-Made using Italian leather and grosgrain ribbon
Available from Distil Union, 39.99.