I currently wear a USB Medical ID Bracelet.
With all of the things I am allergic to (codeine, ceclor, amoxicillin, tylenol sensitivity, latex), I've been wearing one for the last 5 years at the urging of my mom, an ex-roommate with similar allergies, and my GP at the time - with my allergies, the last thing I need is to find myself incapacitated somewhere and have a well meaning emergency medical worker administer something that will hurt rather than help me.
The front of my current bracelet states that I have Crohn's & Allergies and instructs one to look at the back and the USB inside. About a year ago, I upgraded to the USB style when I started taking Humira; mainly because it contains all of the information that emergency personnel could possibly need to access - my doctors' information, my personal information, my emergency contact information, what medicine I'm on (along with how much and how often), my immunization records, my family medical history, and my doctor appointments for the last year since starting Humira. I also find it to be very helpful when I have an appointment with a new doctor because all the information they could possibly need is right on my wrist.