It depends of course on your age and your reason for travelling (private or business), but pants with a bit of stretch to them (not more than 2% or the pants will stretch out of shape, especially at the knees). Make sure to layer with a T-shirt, long arm shirt and a sweater/cardigan. Some flights are terribly cold while others are really hot. Layering will keep you ready for both. Make sure you have shoes on that will forgive your feet swelling, especially if you are on a long flight. Keep belt buckles and jewelry to a minimum to speed up security checks. Mosturize your face and hands and put on your makeup about 30 minutes before landing. A pashmina shawl is my favorite accessory for flights as you can use it as a blanket, an extra pillow or to cover up any drafts that there might be. And it's easy to stow it.