I always wear jeans on long haul flights. I am not a Tracky Dack person and have not owned a pair for 35 years. So for me jeans (I keep wallet and passport in pocket for security) and a Tshirt with a hoodie over the top as I like the whole layers thing. Slip on shoes that I can put on/off hands free for the toilet visits and I do like a cap I can put the brim down over my eyes if the mask is annoying me.
Most of my travel however is domestic and business related so the whole suit, shirt and tie rubbish so I can go straight from airport to rental car and client meeting except when I do a Perth from Melbourne run then I head to the VA lounge and change into the suit there and hit the road.
As an Aside
I find it funny when I check in at the desk wearing a suit I get the "good morning sir" and when I check in wearing jeans I get the "g-day mate". Neither offend me just that people see clothes as uniforms. I regularly pick up medication from a pharmac_ that is schedule listed and when I wear a suit all is good, I rock in on a weekend in shorts and a t-shirt I get asked for ID. Same pharmac_, same script, I am the same bloke, different uniform. Interesting