We are doing a trip this summer from Calgary to Boston and back.
Last summer our trip was from Calgary to Disneyland then up the pacific coast when our children were 4, 6, and 6. We will repeat this trip later in the summer.
We're in a motor home so figure that into part of my answer. The parents switched off driving / working with the children tasks on a schedule. This keeps the adults fresh for both those tasks.
We have more room to have projects, worksheets, books, art projects, than you do in the expedition. I would suggest packing those items in plastic bins to rotate into the expedition. The books of the day are slipped into a canvas bag and the handles are through the seat belt - so it can't get away.
Last year I started them journaling on our trips - . It was a two part process. The first part was them each dictating what they wanted to say. I typed it into the laptop and printed it out using comic sans at 16 pt. Then they copied the words into their journals (spiral books they'd chosen at the dollar store). Obviously this is wonderful for literacy skills as well as fine motor. If they are just starting to write like my preschooler last year (kdg this year) have him write just a sentence at a time, and do the activity a couple times during the day so it doesn't get to be too much.
We don't have electronic games of any kind. They read books and play board games. Having the table makes this lots easier. You might try clipboards. I also subscribe to readinga-z.com and vocabularya-z.com and have those books and accompanying lessons/worksheets printed out and ready to go. Those start at pre-preschool age so it might work for you as well. The books/lessons are leveled which means they build on the previous level. If you do this bring glue sticks, scissors, and colored pencils because there are fun manipulatives as well as the reading. I have their current levels in hanging file folders in a rubbermaid file box with the carry handle on top.
Stopping along the way sucks up huge huge amounts of time. Having snack and lunch items ready to go made a huge difference for us. I could open the fridge and pull out food and everyone could eat while we were going. The children have large sippy cups of water - the ones sold for adults that you press the button to make the water flow - that do not leak. I think they are a liter/quart. We put them on a leash to their car seats so they don't drop to the floor and precipitate "Mommy I dropped my water bottle".
Potty breaks for the little ones used to stop us when we traveled in the mini-van until I always brought along a little potty seat (Bjorn). At least we didn't have to find a restaurant or gas station!
The rectangular restaurant cold storage boxes (Sam's Club - Rubbermade) exactly fit into the storage cabinets of our model. They are clear and stack. These work quite well to hold books / craft supplies / other activities, and would be easy to move between the expedition and the trailer. From their website:
Durable and stain-resistant clear polycarbonate allows for easy identification of contents
NSF certified commercial dishwasher safe, freezer safe
Includes tight-fitting snap-on lid to keep food fresh
Box is 18" long x 12" wide x 6" deep
As far as time on the road each day, we had no problem doing 10 hours if there was not a point of interest stop along the way.
I think random restaurants along the road have wasted the most time - two hours elaspes between pulling off the highway and pulling back on and the food is never as good as what you can make yourself.