Hi! When my kids were 6 and 3, we moved from California to Massachusetts and chose to drive (some said we were crazy, but we actually had a GREAT trip!) We drove for 8 days, anywhere from 8-12 hours per day, AND we only allowed one video a day. After moving, we took two long plane trips a year to visit California family. Anyway, I'll try to throw out a few ideas.
First one, pipe cleaners. It's amazing what can be created with a big bag of pipe cleaners in different colors. You could even make a game out of it, something like charades? Just write up a big list of possible words beforehand, cut them into strips and keep them in a bag for drawing out of. To make it more challenging, make some of those words be verbs instead of just plain nouns.
Origami. An origami book and assorted papers just kept my 10 year old really happy for a couple hours on a plane recently.
Are you into Disney pins? We picked up a book chronicalling most of the pins ever produced so far. This kept the attention of both my kids for a good long time and made for some fun conversation between us on the plane! Which pin do you wish you had? There are some really cool pins out there! Or maybe your kids collect something else - a book on baseball cards, or rocks, or....
Before any big trip, we always make a trip to one of the big book stores. The kids each get to pick out one new book and a couple magazines and/or puzzle books.
I also buy a few different bags of individually wrapped hard candies and dump them in a pile before the trip. Each family member can fill up a small ziploc of the kinds he likes. Then we each have somethings to suck on if we have to wait another hour or more to get to some real food. (My kids are good about this - they don't go overboard on the candy.)
If we're driving, a special treat is sometimes a trip to a gas station that has a really big store attached. It's amazing the different kinds of bottled drinks and snacks you can find at a gas station and nowhere else!
If I think of anymore, I'll post again later. Have fun on your trip!