Pet Stores. If they have a pet tag engraving machine (usually self service up front by the door) they probably have a luggage tag in it too. Something like this



I've usually seen them in black with gold lettering which I think looks better, but they are solid metal, the letters are engraved into it so nothing can happen to it, and they will last forever. I still have some we bought a dozen years ago, and actually taped our new address to because I didn't want to take it off the bag.

They are just a few bucks, and you get them in minutes.

If you want to go a bit classier, most engraving shops can do the same thing in silver or gold tags.