Headphones and earbuds
For long plane rides, you'll no doubt want to listen to music or movies on your mobile device. Get a pair of good headphones if you travel a lot; unlike earbuds, they cut out a lot of the engine and cabin noise. Although it's pricey and a bit bulky, I especially appreciate my Bose QuietComfort 3 when going cross-country or overseas.
The rest of the time, keep a pair of good earbuds handy. Klipsch's Image S3 are very nice in-canal earbuds, with great sound and a nice array of colors. Apple's EarPods fit nicely if, like me, you don’t like the kind of earbuds that insert into your ear canal.