We are planning another road trip in 3 weeks. We done many long ones with someone being a baby. We now have a 12 1/2 month old and a 3 1/2 year old. Our trips are about 11 hours total. We usually break up the drive there and back in half. Drive halfway, swim or do something where we stay and then drive the other half.
I went to McDonald's website and did their trip link (bottom right of the page...kind of hard to find at first). Then I wrote down all the McD's that have PlayPlaces at them from Point A to Point B. We will use that for pit stops. I once heard from someone else to let the kids play while Mom and Dad (& Baby) eat and then let the kids eat in the car. Also know where the rest areas are and keep a map or GPS handy for the last minute stops for the bathroom/feedings.
The DVD player helps for the older ones. We also try to allow a seat open next to the baby for Mom or Dad to sit when it starts to get ugly.
Pack plenty of drinks and snacks that can be easily accessed. I also pack a pouch of toys to be doled out when someone gets bored. I've heard some people actually wrap trinkets and toys for the kids to unwrap every so many miles/hours. Not sure I want to do this.
Put pullups on the recently potty trained and take an extra potty seat if you have space to do it.
Best of luck! I'm sure you will get many more great ideas! I will keep an eye out, too. :)