How long is the flight?
There is a charging adaptor for laptops that Apple sells, its designed to plug into the charging points on airline seats.
You might find that the airline you are flying with does not even offer the charging sockets anyway, I have only ever seen them on Virgin Business Class and MaxJet (sadly now defunct).
+ I don't even think Apple make a charging adaptor for the iPod/iPhone designed to plug into these airline sockets.
If I were you I would buy a simple USB rechargeable battery back, its a small lithium battery that you charge via a USB port on your laptop/desktop and then you can connect you iPod/iPhone to it and it will charge it.
Here is a link to one on the Apple UK site, I have this very unit and have used it many times to keep my iPhone going.
http://store.apple.com/uk/product/TX...co=MTA4NzI5NTM