When traveling with a snake, it is best not to feed it before the trip, the stress can cause it to regurge. It stinks really bad in a car. Best way to get your snakes home from a show is right in the cup they came in. When stopping, if you have to leave the car, I would suggest getting a snake bag, made from muslin cloth generally, or a light cotton pillow case. Put the cups right in the bag and take them with you. Temps can climb to lethal levels in a car within just a few minutes, I wouldn't try to leave them.
As mentioned, something for the snake to burrow in will help it feel more secure.
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Drew Z.
Member, NJHS