I've been riding with a "Road ID" for a number of years now. I would not necessarily put any non-public information on it (i.e. SSN, driver's license #, etc).
I have this on mine:- My name and DOB
- Wife contact telnum
- Son 1 telnum
- Son 2 Telnum
- Med info (i.e. NKA, med 1, med 2)