We moved to Germany from the US when my boys were 1, 3, and 5 years old, and then moved back home 15 months later. The flights were a little crazy.
There are some good ideas already mentioned, but one thing that I liked was that I got them each 4 or 5 small gifts (like a few dollars each) and wrapped them up in wrapping paper. Every few hours, they got to unwrap a new "present." They loved the idea of a new present!