Here's something to keep in your map pockets (if you still have them) or your glovebox (which is probably already too full if you don't have map pockets): a disposable camera, a little chemical snap light, and a clearly written card with emergency information - roadside assistance #s, insurance information, etc. Laminate this card and put it with the camera and light in one of those plastic FedEx type bags that seal shut.

Assuming you're not badly injured, for insurance purposes it's a good idea to snap as many pictures as you can of everything on the accident scene - the damage to your car from different angles, the damage to the other car, skidmarks, the whole intersection, etc.

I think it's better to put this stuff in the passenger compartment than the trunk because of the real possibility that you won't be able to open the trunk in an emergency.