By the time you board the plane, you will be prepared for the journey, and will not have to drink as much water to see you through the flight. Rule number two. Cosy, but also refined and elegant. For men, tailored pants, a collared shirt and perhaps a pullover are likely to do. Not too casual, not too formal and layered to cope with the change in temperature.
Shoes are important.
Many passengers have a preference for throwing them off and getting well acquainted with the airline-provided socks. Again, it cannot be stressed often enough go for comfort and a pair of shoes that will accommodate a slightly expanded foot. Women stay away from heels. Anyone who tried to indoctrinate you into thinking that heels equalled elegance was obviously lying. There is nothing remotely chic about backache, or tripping as you try to manoeuvre your hand luggage up the plane stairs besides, if God forbid you have to use the airplane slide, you will be compelled to leave the Blahniks behind.