I know I am much more emotionally vulnerable on flights, I cry at the movies, often at the most ridiculous moments: Always been a snuffler for Charlie Chaplin poverty bathos but now, one glance from an actor can get the tears running. Crying at Stewart Little. Or Luke.. I am your father. Or Stewie and Peter having a hug. Insane!
I take frequent toilet breaks. I drink a lot of water all the time. It annoys the living bejesus out of everyone but there isn't much I can do about that and having had Kidney stones on an extended overseas trip I never want to go there again.
Kindles are gold. Better than movies mostly, If you can sleep with headphones on or in, then a kindle and gentle music can work wonders. I've slept through 5 CDs of Vladamir Ashkenazy playing chopin before now (actually, copied to minidisc)
But in the end, there's always Temazepam. 10mg. Some people say Melatonin works for them but my partner had horrid florid nightmares and restless legs. You don't need that on a plane.
Avoid over drinking the booze. And, don't be stupid. The crew have a job to do, and it doesn't include being chatted up, or dealing with your feet intruding through a seat on somebody elses space.
(used to do 10 a year, long haul/international, worldwide for 20 years)
I'm on a flight right now. So I guess I also read HN on flights. :-)
I watched some of my favorite movies and would pause the movie after a good scene and reflect on it. It was a fun journal activity. When I returned home, I published some of the journal entires as blog posts.
By the time I got to my destination the first time, I had a severely thorough understanding of Lisp macros. There isn't much else to do, other than look out the window at clouds and ocean, or darkness as the time of day dictates. So I use it to learn things I otherwise "don't have the time for" but genuinely am interested in.
I tend to fast before any flight. This helps me to sleep easily, and also avoid having to eat on the plane. These are helpful as I have some medical issues which make travel complex.
I did it on the way to Singapore and it was, eventually, bliss. No music, no book, no film, nothing. I just sat.