M.M.
We just took a road trip with a 4 year old and 21 month old. The DVD was a life saver. We brought along the Nintendo DS for the 4 year old. He usually only gets to play for 20-30 minutes but I let him play longer in the car and it kept him occupied. For the youngest one I bought a few new cars and a new book for him and when he got fussy I pulled out a new toy. Like someone else said we drove through all naps and when we stopped for anything, even gas, we let them get out and walk through the store for a little bit. I brought lots of snacks with us (more than I thought I'd need). Good luck and have fun!