I left my drivers license (but fortunately not my wallet) at the security gate before getting on a red eye to DTW. And didn't find out until I walked up to the Avis counter, of course.

Fortunately, my hotel wasn't but a mile from the office, and it was fairly mild weather, so I just got some extra exercise that week. The best part was all everyone I was working with freaking out and asking me if I needed rides. A mile really isn't that bad of a walk, folks!