Here's a general idea of how Roadtrips work for us. Keep in mind the longest we've done is 6 hours give or take a few. On the way there the boys don't need nearly as many rest stops or bathroom breaks for whatever reason so we usually only stop twice but this is how roadtrips work for us.
I don't give them anything new/play any games/or get out anything until the excitement of leaving wears off. Sometimes this takes 20 min other times an hour. They'll fiddle through the things they brought in their bags, look out the window, etc. Once that excitement wears off we'll start the entertaining.
Games! Here is a great list/site of roadtrip games. You could buy their favorite board games in a travel edition. One really fun game for the older kids is a digital camera safari. If you have more than one digital camera give one to each kid along with a list of things you're sure to see along the way and see who can get a picture of everything on the list!
Roadtrip bag - as I mentioned in the last post these are SUPER fun for my kids and I've given them something from the bag as I see fit and also done choose one thing each hour (be sure to leave some for the ride home).
Movies/portable games are GREAT but I like to space them out. We actually haven't done any movies the last couple trips and have had no issue missing them. I like to wait until they've exhausted a couple of play options and we just need that little extra time to get to a rest stop.
If you can make time to stop at silly tourist spots along the way. This has also become a roadtrip favorite. Find out ahead of time if the World's Largest Ball of Twine or Cup of Yogurt is on your route and make time to stop. It's a fun photo op and will probably be one of the silliest highlights of your trips.
(I ALWAYS wanted to stop at these dinosaurs in Cabazon - Pee Wee's Big Adventure anyone? but my parents never did so I made sure to stop when mine asked to. My "traumatic" childhood memory had nothing to do with it I'm sure)
If you have the time and desire you can create a treasure map with a little symbol for each stop so they can check them off along the way until you get to your treasured destination.
You could even do some Geocaching (we're doing a post on this soon) along the way!
Take advantage of the rest stops. This last trip on the way home (when they are just a little bit more on edge ready to get home) we stopped a few more times than usual to stretch. This is at a random rest stop in the desert of California and the boys checked out the wildlife trying to find everything that was on the display, threw rocks, ran around and got hot and tired. After 15 minutes they were asking to go back in the car :)
We've listened to audio books as a family or read books, cut or picked out things we want to do out of magazines (my 8 year old loves Family Fun), talked about landmarks, danced and lip synced to our favorite songs (don't forget to take video), colored, drew pictures of each other, practiced math/writing/spelling, told each other jokes... We basically do a lot of hanging out. My boys appreciate the one on one time and conversation and when they are tired of that we move on.
Most of the time we won't go through everything on the way there, but will use a lot more of the ideas on the way back.