My first thoughts were "how were you driving" and "how full did you fill the bowl"? Many people, when they drive, forget about the pets in the carriers who are not strapped in and have no idea when turns and stops are about to happen. Consequently, while the cat may be standing or moving about the car comes to a sudden stop and he goes flying. Basically it's the same with water. You don't need to put much in the bowl, just check it periodically. Cats need water more than food and unless you are going on a drive with no stops I would withhold the food until you stop; dry food adds to thirst. Feeding also adds to the need to eliminate and with no litterbox in the carrier you will have one unhappy camper! When you stop for gas, check the water.