Bringing books for your children on your flight can be a great way to pass the time. If your kids are old enough, they can obviously bring and read their own book. For younger kids, you can bring some of their favorite picture books along, and maybe some good new ones on airplanes, travel and flying.
These days, portable DVD players, and various audio players are also an option on board, and so are different types of apps. For example, the company Tales2Go offers an app for various Apple devices (like iphones, ipads, and ipods) making it possible for your children to listen to any of the stories available in their library. I haven't tried this app myself, but it definitely sounds like an easy and convenient way to bring some stories with you when you're traveling.
Downloading some audio books for your children to listen to on your trip can also be a good way to keep them entertained at airports and on board.
Whether you choose books or audio, both fiction and non-fiction stories travel and airplanes can be a good choice, and can help make the trip more fun and also less scary for kids (and adults!) who are worried about flying or being away from home.
I like The Noisy Airplane Ride
, by Mike Downs, that describes and explains the many strange noises you hear during a flight. This one I'm picking up for our next trip! 
There's also Going on a Plane
, by Anne Civardi that has some very cute illustrations and a humorous take on family travel by air.
For kids who are a little older, or just really into the technical aspects of airplanes and air travel, there are many books out there, for example "All Aboard Airplanes
", by Frank Evans and "My Plane Book"
, by Ellen Kirk.Some good kids' books for varying ages that feature a lot of travel are the Toot and Puddle series, the Tintin comic books, and why not Jules Verne's "Around the World in 80 Days"
!
Another book that can be of interest for traveling kids, is "Storybook Travels: From Eloise's New York to Harry Potter's London, Visits to 30 of the Best-Loved Landmarks in Children's Literature
". This sounds like an awesome travel book for kids if you're going to visit any of the featured destinations.
An atlas or other map book can also be an excellent thing to bring for kids on your trip, no matter how far away or close to home you're traveling, to help explain where you're going. There are lots of these types of books for kids, including "National Geographic Our World", and "TIME For Kids World Atlas"
.