building on the immediate "dogtag" ID idea. There are lots of USB and interactive types. Not good for EMS/roadside, but very helpful IN the Emergency Dept.
Best one I have come across is The Medical Passport
It has a program built INTO the drive, that records info and assists you. Also goes over Living Will type things with pictures, etc. It does not have HIPPA problems because it is self contained on the drive and not on a server or computer, it is on YOU. Password protected medical info can be loaded on it (including photos and scans-EKG for instance) for more in depth for the provider. Emergency info you specify is available for all to see.