We do crackers, cookies, chips, granola bars, and, since both our kids used sippy cups on our last trip, I had six filled and in a cooler for the ride. We do stop and eat our meals at a sit done place (even if it is Mc Donalds) so they have a chance to get out of the car. Also the greatest thing we got was the portable tv/vcr for the trip. I bought a bunch of videos off ebay and that at least kept my older DD 3 occupied and happy (for the most part).
I make enough zip loc bags with these snacks in them to last the whole trip and the whole ride home. We saved a ton of money not having to buy snacks at the resort or parks by doing this.
I am not sure how long your ride is but ours is about 20 hours with multiple stops. When we got home, we were shocked to see what a mess the back seat was. We removed their car seats and found a TON of food. I think no matter what you bring, be prepared to thoroughly clean the car after the trip.