I've seen people use chinese food boxes (you know the little compressed paper boxes with the wire handles?) for sending mice and rats home in, but make sure you explain to people how sensitive they are to heat... and to make sure they get plenty of air, don't sit in sunlight, and if they have to make any stops before going home, to bring the inside with them. They go down really really fast in the heat, and I'm sure anybody buying a rat as food, unless they need it prekilled or frozen, would prefer it stay alive... even more so if bought as a pet.

I've seen rats and ASFs displayed in deep tubs or aquariums, The tubs are going to be lighter for the size, and probably appear cleaner than glass. Depending on how each is ventilated though, one might be better than the other if it is going to be really warm. You can also bring several frozen water bottles in a cooler, and put them in with the rats/change them out as they thaw, to keep them cooled down.