One thing missing from everyone's list - dogtags. Preferably with your name, phone #, Dr's name, phone #. Say you are out and go down for any reason, someone finds you, manages to get you out and an ambulance or medivac chopper picks you up. Are they going to know who you are?
Even if you have your wallet on you, they know your name, but still don't know what Dr to call to get your records, allergies, problem conditions...
Always go hiking with someone you know? Neighbor perhaps? Does he know your Dr? Do you know his? A dogtag will almost always be with you even if you lose most everything else. In an emergency it can be a lifesaver.
There's even a site that sells a polished tag with laser engraving on one side with all kinds of space for info. On the other side you can get a compass or other stuff engraved. (Though if you were hardcore, you'd get the Geocaching logo engraved.)
Just some sites:
www.id-ideas.com
www.roadid.com
www.smartidtag.com
