When we found out we were expecting our third child, we knew the time was right to 'experience' a trip to Disney for our other two children - since a baby would change timing for a few years. Turns out it was me that needed those frequent stops for bathrooms and nausea - since we overplanned for the kids.
We packed those things mentioned, and our two-year old loved the DVD player, even though she'd never watched a movie in her life - and to this day doesn't care for them. She loved having music or silly programs in her view. Also the magnadoodle, magnetic toys, lots of colors and large beads - just things to keep her hands busy. (We also talked about what was to come. We planned specific stops and mentioned early that we were trying to find the ?? and could they help us?)
And we dressed the kids in comfy clothes for bedtime - so they'd be ready for a carseat the next morning - without being in jammies. All of my children need to be 'changed' before heading out the door. We'd get up extra early (like between three and four) and wash up - pack the van - and then, lastly, carry the kids to carseats. Worked like a charm. We managed to pull off those early morning hours of driving and chatting as the kids slept their way into a late wake-up. We would later take mini-naps between us and drove strong through the afternoon naps.
We were on the road for nine days - with two completely on the road - and had very few issues - again, mostly me!
Good luck, and have a great adventure :)
T.