How can you give your immune system a little boost before a long haul flight?

Take a nap: Rest is the best thing you can do for your body before a long flight. During the flight drink lots of water & avoid those little bottles of alcohol. Water will keep you hydrated and ultimately force you to use the restroom. This has the added advantage of forcing you to move about the cabin improving circulation in your legs & preventing blood clots. Don't forget to wash your hands.

No magic pill: Many people are looking for some "magic pill" to "boost their immune system". There is no such pill. However, there is a way to boost your immune system, live a healthy lifestyle. Proper diet, proper sleep- wake cycles, healthy environment, proper exercise are the foundation of good health and good immune health. Supplements should be used selectively to supplement a healthy diet.