We drive from Houston once a year. We use suitcases, and pack an overnight bag that we use if we decide to stay over on the trip down.
We always have a cooler, in which we pack drinks and sandwiches, so we don't have to stop for dinner, at a drive thru or a sit down restaurant. Snacks go in a plastic tub of some sort that the kids can get to at their whim. It works out okay for us.
I always do laundry while down there, so our clothes are clean before arriving home! Love that!! Anything we buy down there stays in the bags we bought them in, and then condensed down into a suitcase or just left in the bags for the drive home.
I found that travelling car games were a huge hit for the kids, but now we have 2 DVD players in the truck, so it's usually movies now and on last trip, DH surprised my son and hooked up his playstation for the trip!! That was a HUGE hit!! Also make them take books, so they can read along the way.
Hope this helps. Ask if you have more specific questions.