1 (a). If nothing else, get the best noise-cancelling earphones you can. I have some in-ear Sennheiser ones. The nearest to the model i have that i can see is the CX500. Comes with a volume control on the cord, different size earplus and if it still has one, an on-off switch for the noise reduction.
I haven't tried any of the over-ear ones, but they can be £200-250 so presume they must be as good or better; but the sheer luxury of sticking the rubber earpiece in your ear and that drone disappearing takes a hell of a lot of stress away. The number one tip. Bar none.
(b) A snazzy sweatband/headband/buff thingy, if choosing in-ear earphones, to stop them slowly working their way out - or being pulled out when you nod off!
(c) Obviously, you chosen music device!! the point with the noise cancelling earphones is, use them all the time, even when NOt listening to music, as you don't realise how stressing the constant drone is until after it has stopped. But if you forget your ipod you'll be sick!
2. (a) A good, long book that you have always meant to read.
(b) don't forget your bookmark!
3. A fleece jacket, for when it gets cold on the plane.
Did I mention noise-cancelling earphones?