I don't think I would bother with carrying a compressor that can reach 120psi. Every one that has been mentioned will be so slow that you won't want to use it. I carry a Harbor Freight pancake compressor. It is capable of over 100psi. And it runs pretty good. I used it to nail down 500sq/ft of hardwood flooring recently, just because it was easier than stringing hose from my shop compressor. To use it on the road I would have to dig out the generator, dig out the compressor, and then wait forever for it to top up a tire. I figure that would be okay in an emergency, to limp to town for example. I guess I'm just saying that you won't find it very convenient. And you can limp to town on 80psi.
If you do get a compressor, make sure you equip it with a fitting that will snap onto a tire stem. Because you're going to be connected for a long time, and you won't want to be kneeling and holding the chuck for an hour.