There are at least a dozen methods of carrying emergency information with you. In these high tech times, I would recommend carrying that information with you electronically, as well as on a piece of paper or in a medical ID bracelet. The electronic method allows for storage of more information.
In this case, I am talking about medical information, next of kin, and other information that you might want emergency responders to find. While my mother convinced me to always have clean underwear, it's probably more important to make sure you have easily-findable information on your body as well.
For those with significant medical problems, such as diabetes or heart problems, a medical ID bracelet is a great idea. Medical personnel always look for those. However, the amount of information you can include in a normal medical bracelet is limited.