I have a 15 year old "wallet on a string". That's what they were called back then. Basically it is a traditional multi-comparment wallet with two small outer hooks that can be attached to a removable strap. I keep the strap attached and place the wallet in my larger pocketbook. In the wallet I place one or two credit cards, a gym club photo I.D card (no address or phone number on it, just my name), coupons I plan to use, plus some cash, loose change, a small comb, and chapstick. It's very compact and light weight.
When I go into a store, I take just bring this wallet, my car keys, and my cell phone. I hide the larger pocketbook under the passenger seat (before reaching the parking space). While I'm in stores or a mall, I keep the wallet strap hanging around my neck and tucked under my arm, and the cell phone and keys are in my pants pocket. I have a pair of slacks with small snug pockets that is ideal for this.
So far, so good.