JDiver

Generally, comfort rules. Loose, comfortable clothing that breathes, doesn't wrinkle easily. Perhaps a track suit for a very long haul / long haul red eye. Comfortable, easy to don and doff hard sole tie shoes - safety considerations require those and clothing that is natural fabric, not synthetic plastic, which is nasty in fire conditions. (Habits from the days I was a pilot, for one thing.)

For would be self-appointed fashion police who might try imposing their standard on me or comment negatively on my choices, given I don't care or comment about theirs, I'd offer two words - and you may properly guess they're not "merry Christmas " or "happy birthday..