I'm fortunate to have no significant medical issues - the cheap dog tag on a neck chain that I wear 24/7 has my name & address and ICE/wife's name and cell number.
Agree that ID/info on your person while cycling is #1 if injury or accident makes you non-communicative. I usually have my wallet in a bag on the bike but the dog tag is always under my shirt.
If you end up in the care of EMS or ED personnel, yes any significant medical info could be helpful but immediate lifesaving care will happen with or without ID or medical info.
Blood type? That info would never be used to determine what type blood is transfused. If there is no time for crossmatching, then type O negative blood is sometimes given.