Make sure to accustom them to some sort of restraint--carriers or something--you don't want them getting scared and causing an accident, or getting hurt if something else causes an accident.
When my friend and I traveled with her cat Skimble, we harnessed him (he'd been accustomed to a harness before), put him in a carrier, and stopped every couple of hours to clip on a leash and stretch all our legs. At first, since he was an indoor-only cat, he was very frightened of the outdoors; and we had an accident when he peed in his carrier, because he was afraid to do so outdoors. (Unlike us, I suggest getting him used to not only the harness, but to using the bathroom outdoors, where you'll be traveling; or else taking a litter box with you, and getting him used to just being comfortable being leashed and outdoors.) We took some treats with us, which he loved; and we'd stick our fingers through the holes in the carrier and pet him, which gave him some reassurance. He yowled some, during the beginning of the trip; he was not used to car trips, and associated them with going to the vet's (another mistake--we should have gotten him used to benign car trips).
The vet can give you tranqulizers and/or motion-sickness pills if your cat still has problems after you pre-train it.
So, basically, our plans weren't perfect; and it wasn't fun for anyone; but Skimble adjusted to the move pretty well. Once we were unpacked, a week later (thanks to my L337 (packing) skillz), he happily claimed the new apartment as his own. Cats do recover from "trauma" like this--whether they'll do it without glowering at you angrily from under the bed for a week is another story.