A couple summers ago I found a checkbook that had a bunch of credit cards in the sleeve.

I called the phone number on the checks and got a fax handshake, so I sent him a fax stating that I found his checkbook, and to call me.
When he showed up to claim it, he asked if I also found a wallet and car registration too. Apparently he pulled out from the DMV with all his stuff on the trunk lid after affixing his new stickers to the license plate. *d'oh!*