Avoid dehydration. Bring bottled water on the plane. Make sure to purchase bottled water after you’ve gone through security.
A small bottle of soothing eye drops such as artificial tears is a welcome relief. Keep lips hydrated with lip balm. I keep both in a small sandwich sized zip lock bag that I put inside my quart sized zip lock bag for security. Once I’m through security, it’s easy to pull out just what I need for on the plane.
Have back issues? Bring a self inflating seat cushion to support your back and hips. Neck issues? Bring an inflatable neck collar, so that no matter what position you’re in, your head is supported when dozing.
Many people complain of headaches while flying. Preventing dehydration helps but so will noise cancelling head phones. That constant drone of the engines is greatly reduced and you won’t be subjected to someone else’s conversations. A cool eye mask blocks light and reduces headaches and eye puffiness.
Think about making it easier to maneuver around in small rest rooms. Wear loose fitting clothes without belts. Shoes that are easy to get on and off and allow for a little swelling are also a wise choice.
With a little forethought, riding coach can be a little less uncomfortable.