The airlines (or FAA) prohibit using active cell devices on most flights.
The ipads have "airplane" mode which turns off the wifi and 3g circuits, so the ipads are safe and legal to use in flight.
Your options are:
1-Download movies, videos etc, before the flight for in-flight viewing
2-Download books or other reading material before flight
3-Newspapers & magazine apps sometimes allow downloading for later viewing.
4-Thousnads of apps, games, etc allow for offline use.
To test what apps, etc allow off-line play or use, you can go to airplane mode in Settings at any time to disable all data communications prior to your flight and confirm they work off line.
Good luck....
