I got a flat tire, and no wheel lock nut key. What do I do?

Steven P has the technique, although I use 6 point sockets. They have to be good quality so they don't split, they produce sharp metal curls from the lock nut as you hammer them on, so watch your fingers. The nut has to be driven out with a drift and vise when you are done, but you (or any thief, for that matter) can get the nut off the wheel about as quickly with a socket as with the proper tool.