We have a lot of those five gallon plastic buckets that paint, drywall plaster etc. comes in. One of those makes a great container for a wash kit, if size isn't a major consideration. Good to have around for extra water carrying capacity, or as an emergency toilet. If size is a factor, the tupperware sounds good.

+1 on the camp suds. That stuff comes in handy in a lot of situations. Even camping trips.