When flying international F or J, we always dressed business casual and I'd bring some lounging pants and a sleeping top to change into at night. Most of the time we were flying to Asia or Oceania, so fairly long flights. Domestically, nah, just Levi's and a collared shirt. I've never flown for business, only visiting friends or going on vacation. I know my dad, who wore a suit every day, looked forward to vacation travel to get as far away from that suit as possible.