Lots of great info already shared. I also am a ATHLETA fan and have several of their pants for travel/long flights. I find them extremely comfortable, they form to my shape and are NOT binding at all. They hold well up and don't loose their shape. They are excellent for stains and or spills and dry quickly.
I also layer - typically a top/tshirt with a wrap or light/medium jacket. I prefer easy, slip on and off shoes for the airport and have a pair of socks handy in my carry on bag for the actual flight.
Here is a sample of my travel gear/outfits
https://youlookfab.com/finds/c.....ction=7526
Good luck and enjoy your trip!