Rent (and make sure you download) a movie from iTunes
If you prefer more options than the limited catalog of newish flicks streaming on the impossibly tiny screen tucked into the headrest in front of you, consider renting something you'll actually want to watch ahead of time.
You can virtually rent tons of new releases and older fare via the iTunes Store for as little as 99 cents apiece. Once you start watching, you'll have 24 hours to finish before the file disappears from your device (the rental period is 30 days otherwise).
Pro tip: Figure out what you want to rent and "download" it on a speedy Wi-Fi connection before you leave for the airport, making sure it's fully downloaded onto your machine by clicking the Cloud download icon once you confirm the rental. By default, iTunes sets rented movies to stream from the Cloud when you hit "play" (which presumes you have an internet connection), so double-check your rental is fully downloaded onto your device ahead of time or you'll get an error message when you try to watch at 30,000ft sans Wi-Fi.