I never thought I needed noise-canceling headphones. I always focused and ignored outside distractions but didn’t know what I was missing. I never knew how much noise trains, planes, subways, etc., generated until I blocked it all out with a pair of Sony wireless headphones, specifically the Sony WH-1000XM3s (newer version linked below). I now feel much better rested after traveling (sometimes even catching a couple of Zs), hearing more of what I’m listening to, and staying focused longer. The battery life is fantastic (30 hours with noise canceling), they support fast charging, and they’re wireless with the option of going wired with an included cable.
These go against my “pack light and pack slim” words of advice, but if the flight is over 3 hours, I’ll either clip the carrying case to my backpack with a lockable S-Biner (when one-bagging) OR pack them into my backpack if two-bagging (backpack + duffle or carry-on).