Do you think it's worth wearing military type dog tags?

What information would you put? I think it traditionally allows five lines with 16 characters including spaces.

- Is it really relevant to include your blood type today?
- Is it relevant to include the year of tetanus shot?
- Personally I don't have known allergies except for cats but that would be a good addition.
- Would you put your social security number (I don't think so)?

Which material is best among them: stainless steel, solid brass, pure copper or aluminum? Is it better with a rubber silencer?

Thank you
Frankie