Comfortable Clothing
Have one thing less to worry about: Wear something comfortable and look smart as well

A cool cap
A light beanie in cashmere or wool, or your favourite material,can help you through different climate zones. Sounds from the outsid e might be muffled a bit, so you can relax more. If you have a Bad Hair Day, you will be covered!
The scarf
Oh, my favourite travel accessory. I prefer the "Pashmina" style scarfs in cashmere or wool mix. They must be light and easy to roll. Sometimes it can be a bit cold when you board the flight. When you sit down in your seat you can use the scarf as a little blanket. Or roll it and use it as support for your neck.
Sweaters
Choosing a sweater in sted of a shirt gives you movement and comfort. Pick a good material. Layering up is always good.
Jeans
Yes, jeans is a perfectly ok garment to travel in, as you can see maybe 70% of travelers use. If you choose a version with lycra or another elastic fibre, it will show a better fit, and be more comfortable when you sit down.
Sneakers
Try to find a pair of sneakers that is easy to slip in and out of, and that are not too tight. So good to wiggle your toes and let the air out.
Compression socks
Search for socks, knee-highs, that will give you support during the day of travel. Compression socks.