Do the medical alert thing- you can actually get red dogtags with the info printed on them. Pacer has one (needs new ballchain) rather than the bracelet. You can still register through the medical alert deal, but dogtags are easier and safer to wear in many cases.
The patch is a good idea, just make sure the people you are playing with (at least some of them, I'm not saying scream it from the rafters) know it is NOT part of a costume or a joke. Do carry something with you like others recommended too.
Finally, listen to your body. If you suddenly start feeling like you are bottoming out or something get out of the game. Take a moment and treat yourself. Games are just games, there will be more time to play.