Stuffed Suitcase had this to say, with a few comments of my own, of course! Most of this applies only to trans oceanic flights, and most cross country flights.
Comfortable Pants I would say this generally does not include denim for men or women, unless they are the stretch variety. Women can wear leggings; men are a bit more limited. But I have stopped wearing Bermuda shorts on long flights since my legs get cold and would be exposed to “things” mostly invisible. I actually found some nice stretch pants at Sam’s Club that travel quite well, never wrinkle, and can be hand washed in my hotel room.
Shirt I prefer a long sleeve shirt, even though it tends to wrinkle a bit. I am not a fan of T shirts, since they look a bit sloppy. Sometimes, a nice polo shirt also works well, when heading to a warm climate. But planes can get a bit chilly, particularly on long distance flights. Women can carry a blanket scarf, but guys need a light sweater or sweatshirt.
Shoes Well, rule number one, never wear flip flops. During an emergency or fire, you will not have a chance! I generally opt for a nice pair of sneakers or comfortable walking shoes. My new favorites are the Hoka Ones. In Biz, the airline provides disposable socks. But never, I repeat never, go barefoot!!
Support stockings I started wearing these last year and found that I feel much better when I land. I wear the disposable airline socks over mine.
Hydration Regardless of where I sit, I always carry a water bottle. Always! Contrary to the experts, I do have a glass of champagne or sparkling wine in Biz class. And sometimes a glass of wine with dinner.
Move I try to take several walks, if only to use the toilet. I try to stretch my back and hamstrings and Achilles as well. Also, the benefit of having a lie flat seat allows better overall circulation.
Long flight secrets I always carry pain meds, mints, sunglasses, ear plugs, a paperback book, and an energy bar.
My secret weapon I try to bring a few treats or some products from our farm cooperative to share with both the flight attendants and restaurant staff while on my trip. They enjoy our Sun Maid raisins, instant Starbucks, or See’s candy.
Now you know all of my secrets!!!