Digital cameras are just the right size to slip out of your pocket on the subway. While aspiring detectives will enjoy trying to track down the rightful owner by identifying restaurant interiors and concert snapshots, it is a lot easier to keep a photo with your phone number on it. I think a handwritten note says it best.
Many cameras allow you to lock a photo on the memory card. I recommend locking this one so that it is always your #1 photo and doesn't get cleared like the rest of the photos. This screen would also be a good place to put anything that emergency workers would need, like your blood type, drug allergies or organ donor status.
Until you are carrying around an iPhone or personal GPS unit, your camera can substitute. With modern 5-12 megapixel cameras, you can fit a lot of detail on a single photo, and most cameras allow you to zoom in on photos for a closer view.
If you are new to an airport, snap a shot of their floorplan in case you have to find gate L45 in a hurry. This trick is also good for keeping a shot of the Metro system.
Lately, when checking an address online, I've been snapping a photo of the Google Maps screen as an insurance policy. I've also found it useful when describing what part of the city our new house is in. This would also be good for people who find themselves challenged with describing where on earth to find Laos.
These tips are even more useful for camphones since one is more likely to be carrying a mobile than a digicam, right? =)