License, insurance card, credit card and organ donor card.
G*d forbid, but better to have it and not need it than vice versa.
I keep those four cards and about $20 in a small ziploc bag that goes in my jersey pocket when I'm cycling, dry bag in the 'yak, fanny pack when I'm hiking, or just gets jammed in whatever purse I'm carrying. That way I don't have to pull them out every time.
RoadID seems like a good idea, but I'm just not convinced of the security of their data. I know they make all the right noises, but still. I doubt they have the same kind of computer security techs that, say, a bank or insurance company might have, and yet they want me to entrust them with the same data that I give my bank and insurance company.