[gumby]

If you don't carry a wallet or other ID (I rarely do myself):

Tape or p-touch your name to the back of your phone (esp handy for people like me who always have to spell it) and somebody else's phone number (the number of someone who can help if something happens to you).

I include my email address too. Then if someone finds my phone, or me prostrate with my phone, they can get in touch with help.