Maybe you're not an avid reader, but once you're stuck in the middle seat of a plane and napping is all but out of the question, you'll be surprised how much reading you can get done.
1. Because planes are loud.
2. Because flight attendants don't care if you're sleeping.
3. Because in-flight movies, downloaded podcast episodes and perfectly-curated playlists are truly a saving grace.
Let me reiterate: Flight attendants don't care if you're sleeping. Those lights will go up at random, and often.
Maybe I was just brainwashed by my mother, but I refuse to board a plane unless I have gum on me. I'm convinced my ears will never unpop unless I'm chewing a piece of Orbit.
Do not, under any circumstances, stuff your neck pillow into the suitcase you plan on checking. Sure, it makes it easier to carry, but if you leave the pillow where you can't reach it once you're hankering for a nap, you'll be sorry.
That air quality is no bueno, people. Take care of your skin while you're up in the air!
Do you want to stress about spilling your little cup of water while it balances on the tray table? No. Pack a reusable water bottle, keep it empty while you go through security and find a water fountain by the gate.
It doesn't hurt to keep things like a spare pair of contact lenses, deodorant and a toothbrush -- even an extra pair of clean underwear -- in your carry-on. If you get to your destination, but the rest of your luggage doesn't, at least you'll be covered for a bit.
Maybe you're not on a plane with a power outlet (in which case, maybe invest in a portable charger), but chances are you'll drain your cell phone (or laptop, or tablet, or e-reader)'s battery pretty quickly while in-flight, so it's a good insurance policy to keep your chargers in your carry-on instead of checked.
It won't take up as much space as a whole sweatshirt or entire blanket, but it'll keep you warm when you cannot, for the life of you, regulate your temperature on the plane. Plus, you can wear it if it doesn't quite fit in the bag, and it won't count as an extra item.