I have the neck version with:
Name
Year of birth (at the hospital that's useful to distinguish you from another patient, to recover your file if you've been there before, etc.)
Three emergency numbers
NKA (No Known Allergies)
Blood Type
ORGAN DONOR (that's very important to me - no full legal value in most jurisdictions but good indication to the docs and good conversation starter with friends, family, any other people) (not that I wish to get to the point where I have organs to give, but if I do get there, I want to make sure they don't go to waste if there's anything to save)
I'll order new ones because one of the numbers have been updated, and my sweetie doesn't have one yet.