We don't do a lot of traveling in the car. The longest drive that we've done thus far is 3 hours. It's not long but still long enough for a 6 year old to get antsy. So this is what I pack into her backpack: lots of snacks, books, a writing tablet, her pencil box with crayons, markers, and pencils, her Nintendo DS, and last but not least or iPod. Sounds like a lot of stuff but if you knew my daughter you'd know that all of this was necessary. She has a short attention span and need many things to keep her occupied.
On her iPod, we have the music that she likes to listen to, TV shows that she loves such as Suite Life of Zack & Cody, Hannah Montana, and Raven, her favorite movies, and audio books. Right now I just have the Harry Potter series but will be uploading Junie B. Jones and maybe even Spiderwick Chronicles.
Before we had the iPod, we had a portable DVD player. We lugged that thing around with at least 5 different movies every time. When the DVD player broke, we started using my laptop. Thank goodness for the iPod, it's smaller and takes up less space.
When we travel to Hawaii, we pretty much take the same things. It's a 5 hour flight so keeping her entertained is a little more difficult. On the flight, she prefers to write and color so I make sure there are lots of paper and coloring books. She has her own carry on bag with all of her ammo.
I realize that not everyone has a Nintendo DS or iPod but there are other options out there to keep the children entertained. There are lots of games that come in travel versions. Playing cards are also an option that will keep the kids busy. Keeping the children occupied and entertained on long road trips or air travel will not only benefit them but also the parents.