The Lululemon men’s range is by far the most comfortable long-haul travel attire.
Literally a walking cliche but may as well own it.
100% I own enough Lululemon men's gear and have zero regrets - for longhaul flights nothing really beats the comfort of Lululemon/Prana pants. And they are super functional - pockets with zippers are super handy for AirPods, Passport, wallet etc.
Or Hydro Flask if you’re down on your luck in the valley