My flights are usually 12+ hours long, so my tips don't really apply for shorter ones.
I load my iPod with relaxing music (think no lyrics, natural sounds and some of Aphex Twin) and a few audiobooks (the Harry Potter series read by Jim Dale is one of the best). That takes care of the background noise and gives me a chance to sleep.
I also carry some individually packed moisturizer (ie. Urban Therapy by comodynes.com - popular here in Spain).
When I'm flying out, I don't put make up on in the morning, so my skin can breath a little better during the flight, and I apply it 1 hour before landing. Airport security made this a little harder, but I bought some small containers and made my own tiny make-up kit.
I hate hate hate airplane food, so I eat a meal before boarding and I bring my own snacks. Nothing salty or greasy, as that would make you more dehydrated. They'll give you some water in-flight (2-3 glasses), but not nearly enough. Carry a small bottle of water.