Long trips always mean that my care will be trashed with food- but food makes the little traveler happy! I like all your other ideas that you have- although I have learned not to go with coloring crayons- kids color on stuff and they melt. here is my little kid travel arsenal:
Magna doodles- they never run out of paper or loose their crayons!
audio books/dvds
some regular reading books
stuff from the dollar tree that they do not get until we are in the van. Finger pupets, a new book, a squishy ball- whatever! I usually get two or three items per kid and hand them out during the trip.
Food! I go and buy little things that the kids do not gt very often and/or really like. Animal crackers, popcorn, fruit snacks, dried fruit, granola. And a box of zip lock sandwhich bags. I then pre make a dozzen or so snack bags that I can throw back there as needed.
Oh and I also tie their sippy cups on a long enough piece of ribbon so that I can attach it to their carseat strap but that they can get it to their mouth to drink. That way they can not throw/drop their cups.
I would also like to state that I try to do a good chunk of driving while they are sleeping so maybe leave around 3 or 4 in the morning. Earlier is better than later on that one as the later into the morning you go the less likely they will go right back to sleep.
I have driven across country several times with my kids as well as mini trips all over- I have 5 children between 6 months and 8.