People ask about this from time to time, and although it sounds like a neat idea, the general consensus seems to be that in practice, no ER staff is going to use it. I personally would not plug some unknown USB drive into my computer. I seriously doubt that any hospital's IT policy would allow it either. And a USB drive certainly does you no good as far the ambulance crew is concerned.

IMHO, you're better off with a Medic Alert bracelet/pendant and keep your info up to date with the company.