You really need slipper socks for the plane, you take you shoes off and have a stretch and bare feet and your socks can feel yuck after a big flight.
Actually I find that taking your shoes off is not a good thing on flights, especially if I'm in my hiking boots (my heaviest shoes) because my feet swell and getting back into them at the other end is annoying. I did this once, the taking off of the shoes, and couldn't get my shoes back on and had to leave the plane with slipper socks on, wait for the swelling to go down enough to put the boots on so I could leave the airport (it was snowing at my destination).