Ha! Just got off a 30 hour long-haul series of flights. Had a while to view everyone’s travel clothes choices and do my thinking! Was flying from origin 32 degrees (humid), transit was 45 degrees (dry heat), finishing at 11 degrees (winter storm). Not easy!
Pinterest is a great research tool for this, by the way (search ‘long haul outfit’).
The only thing I’d add to their general advice (usually leggings, tunic top, waterfall cardi, slip on shoes) is that I prefer linen wide-legged pants with fold-over waistband instead of leggings. Roomy, not sweaty, more stylish. I also always wear a long cotton scarf. Handy to keep your main outfit clean and extra warmth in air-con situations. I also pack clean spare knickers to change into at the halfway point.
So my travel clothes today were: slim fit chambray trench (to low hip, good to carry essentials in pockets), thin navy double tee with long sleeves/tank, olive linen long wide-legged pants, blue/white/olive infinity scarf, compression knee-highs (hidden!), blue/white adidas slipon sneakers. Smart but super comfy.
Always amazed by people wearing high heels and tight skirts. Or going the other way and wearing essentially pajamas. I’m sure that neither of these options elicit much respect and assistance from airline staff (on the ground or in the air). On long-haul, you need all the help you can get!