Puff and I just got back last night from our second cross country 4,000 mile trip, this one to Oregon (the first was to VA & VT).
Puff has her regular city license and rabies tags (both metal, I put silicone rubber glue on them to hold them together so they don't jingle) plus 2 round plastic tags.
A red one is engraved on one side:
FOR REWARD CALL
and on the other side:
(The second phone is my cell phone #.)
(A second, yellow tag is engraved on one side: "Genuine Official State Licker License" and on the other "Officially Licensed Co-Pilot")
I cover the surface of both plastic tags with clear plastic which I renew periodically (it reduces wear).
On trips such as the ones we've just made, I attach a luggage tag that says "If owner is unavailable or incapacitated call....." and it lists my niece's # in Vermont, two couples in Kansas (one of which will take Puff if anything happened to me while the other holds a check from me made out to the first couple for $1,000 in case money is needed for medical treatment or travel). It also lists her vet (Kansas State CollVetMed Tchng Hospl) and their phone #.