Just as a follow-up on this, in the end I took one SLR (a Ricoh XR-X, plus 28, 50 and 70-200 lenses) and an Olympus XA, plus a bag of random film - the ones I used were Fujicolor Pro 400H, Lucky 100, hand-loaded HP5+, and Elite Chrome 100 (eta: also a roll of T-Max). I've only developed some of the HP5+ so far, but that seems to have come out rather nicely, though the scenery shots are underwhelming so far. I'll admit to being a bit of an HP5+ fan anyway.
If I were to do it again I think I'd take something in MF and a compact 35mm for snaps and street (either the XA or maybe a Trip). The XR-X is a good camera, but apart from entertaining myself with the long lens taking pictures of other cars and roadside scenery during the drive from LA to Vegas, I rarely switched from the 50mm prime. MF would have been much better for taking pictures of urban landscapes.
The old town in Vegas seems much more interesting than the newer parts of the strip, particularly if you like signs, which I do. I wish I'd spent more time there. I also wish I'd spent more time scouting around at night with fast film for street shots in Vegas - there's not a lot going on in the day on the strip apart from badly dressed folk wandering around drinking beer. The Belagio fountains seemed a good place, though, as you can hang around in the shade under the trees and watch people. A tripod and MF would have been great for nice night shots of neon, too.