when we have to transport our snakes we've used multiple snake bags, delicups, small rubbermaids, a heating pad and a cooler. we also keep a thermometer in the cooler to keep an eye on the temp for too hot/cold.
you may not want to feed them before the trip due to temp/stress issues.
another thing to consider, are you making the trip in one day?? or are you staying overnight some where?
wandering would be really really bad... too easy for them to get stuck under the brake pedle or wedged under a seat.
less stress for them to be in a nice dark box/cooler that's a comfy temp and not out and about