Before any of these "emergency" tools are really useful, there needs to be an extremely standardized approach. First Responders cannot spend the time trying dozens of different approaches to try to find information.

I really think the dog tag is best. If you have complicated information then put instructions for recalling that information on the dog tag itself. If you really want to go fancy, put a small USB drive, with only emergency information, with the tags; however, it may not be looked at due to fear of an attack through the USB.