It is no secret that one of the most important aspects of traveling is to make sure that you wear comfortable clothes. After all, airplanes can be uncomfortable enough as it is, so you need something that will help you get comfortable in an uncomfortable situation. That is exactly what you should wear: pants that you can easily pull on and off and that have a flexible waistline that stretches.
That makes it easier when it comes to going to the bathroom, and you also don't have to worry about becoming bloated and uncomfortable in tight clothing.