Way, if you don't *have* to take a cat on a car trip, you really should avoid it - you'd be surprised at how you can find petsitters by asking people you know. The best petsitter I ever had (she even cleaned the house) cost me nothing; she was just happy to have time away from her live-in boyfriend from time to time, and she actually stayed at my house for the whole week. Others will come in and feed, clean litter box, etc., and hopefully spend some time just being there so the cat doesn't think they're all alone.

The cat is happiest being left at home. They're so territory-focused, home is everything to them. And there are many opportunities for a cat to get lost and hurt in a flash while traveling, most especially when you make stops for rest or to stay overnight. It's such stress on you to worry that someone might accidentally open the door and bam! kitty goes off. If you leave them behind with even minimal catsitting, you'll feel much safer and so will she, and you have someone that you can call, too, to see how she is. When you get home, you only have to put up with an hour or so of "Oh, I don't actually know you, you are a stranger to me, yet somehow I disapprove of you anyway."

If for some reason you do have to take a cat on the road, usually what states that check want is a vet's statement of up-to-date vaccinations and rabies shots (not within the past week, but more recent than a certain number of months, and this does vary by state) and that they've been examined and found to be in good health.