Last year I gave up soaps and foams in favor of shave oil for my travel kit. It worked so good it's all I use at home too. Best thing I've ever used for a good shave. You get about 40 shaves out of a tiny bottle smaller than a bottle of eye drops. I don't shave every day so I've only bought 3 bottles since last year and one of those was for my travel kit. The best part is that there's no messy soap to rinse off. Just wipe off any loose hairs and you're good to go.

http://www.cromwell-cruthers.ca/cromwell-cruthers/

addendum: I don't know how well it works with a straight razor. I plan to try but I don't want to buy one just for that...trying to find a hand-me-down.