several times to Disney. We drive 2.5 days and believe it or not, I LOVE IT. We stop every 2 hours-not negotiable. I run the kids around the park and make them go potty. They earn 'spending money' by being well behaved and cooperative and one a day we stop at a
Walmart-K-Mart type store and they can get a goodie. (generally the cheapy toy I would never approve of any other time-even if the plastic cowboy and indians won't last long, they will probably be lost on the drive anyway and it is something they don't have)
I stock up on 'art' stuff we don't usually have or use. I buy a dry erase board and pens. I will get dark construction paper and chalk. Depending on the age of the kids, there are some self contained toys by Little Tyke and Polly Pockets that I might buy and pack to bring out when they are particularly good but I can see that deteriorating.
I pack FOOOOOOOOD Carrots, apples, crackers. We also have candy, cookies, etc but I find that the healthier snacks go much faster than the junk. We also buy at least a case of bottled water and usually pick up more on the way. Again, there is soda in the car but the water goes very fast.
We usually take a book or two that sounds good to all of us. (Invisible Man, Journey to the Center of the Earth, etc.) and DD gets hoarse reading out loud. Books on tape don't work the same because we can't interact.
I definitely agree with the pool. One time we hit bad weather and had to stop without a pool. DH hid in the bathroom while the kids jumped on the beds and ran around the room until they were tired and could sleep. I didn't know if DH would survive.
The only other 'secret' is to stop. When you see a beautiful site or the kids want to walk in the stream, stop and let them. The trip is much more enjoyable.