Definitely get a carrier, or even better a crate that can fit food, water, and litterbox if you have a seven hour drive. You do NOT want a cat freaking out in the car, and you don't want him peeing on the floor either. Just be sure to have blankets available to cover the crate or carrier, which will help him feel more secure. This doesn't mean that you can't try holding him on your lap (or whoever is NOT driving) for part of the drive, just have a plan B in place for when it doesn't work anymore...