I drove 2 days with my poor old man cat. He was 18 years old and was in remission from bowel lymphoma -- he'd been diagnosed 2 years earlier! Indiana to Orlando ... the vet gave us valium for him, but he didn't respond well to it and I should have remembered. It just made him do the same things he was doing, only slower and dopier. We found a pet-friendly motel, but he wandered all night calling, climbing up on things and falling. He was hard of hearing too, so that was pretty bad. I was up all night, following him and giving him a little tap every time he started howling.
We'd stop every few hours (DH was driving the moving van) and I would let the cat out of his cage to wander around the car, use his litter box, etc. He was riding "shotgun" in the front seat so he could see me.
All in all, he made the move very well and enjoyed six months of retirement in sunny Florida before he passed away. He was a great, punky little tabby.