I am an experienced animal trainer and handler with over 30 years experience....yeah sure, I may be a Limey but.....
1. Keep The Cat In The Carrier During ALL Travel Time...
2. When you stop for a break on the road, check your cat and if neccesary let it into the vehicle to do its "rest stop" if it needs one...make sure windows and doors are SHUT, your cat is in a strange place and may panic...
3. YOU need to be watching the road - NOT what the cat is doing, shut in its carrier it is safe, YOUR Driving will be safe...
4. If the cat is not used to being in a vehicle offer only tiny amounts during the trip, make water available ONLY at rest stops...
5. Turn the carrier so that the opening end is facing the seat or a bulkhead or other surface where going under bridges etc will not startle the cat as it wont see them coming...
6. If the carrier is located on a seat use the seatbelt to secure the carrier in place just as securely as you would a child...
7. If the cat appears to be panicking dont check on it straight away, if ignored it will settle very quickly, if it does persist over say 50 miles then stop and check on it, but do NOT open the carrier, if the cat is stressed it will not think twice about attacking you and out the door and gone in just a few seconds...Keep The Carrier Closed unless all doors are closed and windows too, a medium size cat can get through a window gap of around 3 to 4 inches-dont take a chance with it... It comes out just to take on water and if it does not use the "rest stop"/litter tray within a minute or so then it does not actually need it yet...it will hold its water for anything up to 12 hours if it is scared...At ALL times keep it in the carrier...a stressed cat is best contained for ITS safety and for YOUR safety...
I have travelled cats all over the world without ANY kind of incident during travel, Cats can safely go without food for well over 24 hours without any detrimental effects on the cat...Water is only offered during rest stops and taken away during ALL driving times, DO NOT leave water with the cat - this is because of spillage, NO cat wants to be doing any journey lying on a wet bed...
I hope this helps in you making the right choices on your journey...Have a Safe Trip.....