First, always get a flu shot. We travel internationally a lot and get flu shots every six months. If you can travel in F, do so, less people and they are a little farther away.

Wash hands, wash hands, wash hands, and train yourself to not touch your face...eyes, nose, mouth. Bring the strongest antibacterial wipes you can buy. I prefer Costcos and Lysol but will also use WetOnes. The # 1 dirtiest place is the fabric bag on the seat in front of you. Just don't use it. Use antibacterial wipes on seat belt, arm rests, pull down tray, basically anything you are going to use. After you have done all this don't forget to clean your hands again.

Stay hydrated, but I buy my own water, soda, juice, or whatever I want sealed in a bottle. I do not drink out of their glasses.

All of the above is not because I am a hypochondriac, but I do have a compromised immune system. I rarely ever get sick.