DH and I spent 28 days in our van with three kids ranging from 4 to 10 as we drove from MA to CA and back. It was a 7,000 mile adventure. One of my boys has ADHD and the other has IDD (which is a form of ADHD).
Each kid was given their school backpack and allowed to pack it with treasures. To keep everying thing contained they put their toys in ziploc bags and these:
http://order.tupperware.com/pls/htp...tegory_code=10201&fv_item_number=P10055426000 Which are awesome for packing small toys as they open and shut easily and provide a small playing surface. The kids were only allowed to take out one toy at a time. Things they packed:
Books and comic books. Comic books are great for the older kids because there's reading but also lots of pictures to look at. My oldest liked the Archie comics at the time. My youngest is now 10 and likes Looney Tunes.
Little green army men (for the girl you could polly pockets)
Set of small plastic animals.
Matchbox Cars
Balsa wood airplaines with propellers - which the oldest would make and they would then fly in the breeze of the open window.
Legos
DS in case with games
Small stuffed animals.
I also picked up some small foldable packable playsets for them. They each had one and it went under their seat along with their backpack.
The whole point of our trip was the drive get out and see new things explore new territory so when it was all new territory (so say after 4 hours of corn fields the landscape changed) we also used to make them put everything away and look out the window at the scenery and talked about what we were seeing.
We were traveling for many days so we made it a point to stop if we were going to be in the car all day to get out at least once to explore. Often it was something simple like getting out at the "scenic view" rest areas and taking a look - a couple of times it was a public playground (at a mcdonalds or a park). A short simple break between 20 - 30 minutes can work off the restless legs and stop the whinies.
We mostly camped but if we were staying at a hotel I tried to find one with a pool so they had a way to be active at the end of a long day.