For temporary stuff, you could bring your heater and plants and conditioner and stick it in a fairly large plastic container, like $5. How large is your choice.
In the car, I would also put him back in the cup you got him from. Since it won't completely dirty and left alone like a good majority of pet stores, he should be fine. He will probably go pale and whatnot.
Or, you can get an ever larger container, line up with something soft and put the smaller container inside it (incase it spills), and fill the smaller container with water and stick him in there... in my (parents) car, we have an adapter so I would be able to also put a heater in there. I would completely duct-tape down the wires to prevent any pulling. But I wouldn't do this unless you reaaaaaally trust yourself and are up to it.