Noise canceling headphones. I swear by the Bose Quiet Comfort series. Personally I still have the 25 model (with a third party Bluetooth dongle), that way when the battery dies I can simply swap it out, takes simple AAA ones.

Else I'd recommend to bring slippers to wear during the flight. Feet tend to swell up a bit, so wearing shoes is uncomfortable, and walking in socks as many people do is not exactly hygienic, especially in the bathroom (seriously, who does that???).

I'm also freezing easily, so I'll bring a thin scarf to protect my neck from the long exposure to low temperatures.

Lastly, have a set of fresh underwear, t-shirt and wet towels in your hand luggage, along with a toothbrush & paste and deodorant (make sure the volume is hand luggage capable). Then about 1.5h before landing, lock yourself in a bathroom (ideally the ones in the middle, they are a bit more spacious), strip naked, give yourself a through wash, change of clothes etc., and land arrive somewhat refreshed.