I wonder if emergency rooms will just treat you and then worry about ID later. I had a (non-bike) sports injury that required a trip to the ER. One of my teammates brought me in and I had no ID and no proof of insurance. I had a mild concussion so I was even a little fuzzy on some of my personal info. I was able to come up with the important stuff (name/address/etc) but, I couldn't remember my personal physician's name for instance. I had never been to anything associated with that hospital system so I wasn't in their computers. They treated me and sent me home with forms I could fill out and fax in with my insurance info later. I suppose if it turned out I didn't have insurance, they would have tried to get the money out of me personally.

I haven't totally learned my lesson. I always carry ID if I ride alone. If I'm riding with a group, I sometimes get lazy and don't pull it out of my wallet to put it in my saddle bag. I think it's time to make a copy and always keep it in a ziploc in my saddle bag.