The following suggestions were made by Moira Allen in a post to the Feline-L discussion group and are printed here with her permission. Do not leave a door or window open so that they can escape. If you do decide to take the cats outside, do so on a secure halter and leash. Unfamiliar water often causes diarrhea. When transporting the cats, make sure they are in a secure crate or cage.
Cats can travel together in a single crate or separately.
If the cats aren't accustomed to car travel, don't be surprised if they spend most of the journey yowling. Cats also become carsick VERY easily. Be SURE your cat has adequate identification. Make sure it has a collar with an ID tag that clearly identifies the cat's home. Having microchip ID is also a good idea.