There's an old thread that has suggestions from an actual ER doc. What I can remember, some of the things she said

go with the wrist band - the shoe, ankle etc are much more likely to be overlooked

contacts, contacts, contacts - the more contact info you put on it, the better

don't bother to put your blood type on it - you'll never get blood without being typed and matched anyway

they are unlikely to look at the interactive portion of it, it's what's on the band that's most important

leave off the pithy phrases and put in another contact