I travel a lot interntionally so I have a kit I carry along for emergencies. It inclues two rounds of Tamiflu, two rounds of cipro, two rounds of Zithromax, dental items, pain-killers, etc.
I do the flu shots, comply with all recommended innoculations by NIH for the areas I will be visiting, try to avoid stupid items like questionable water at distination, ice cubes, street food, etc.
I have established US travel physican emergency numbers that are available 24/7 but which I have never had the occasion to use.
Of course I follow common sense procedures like getting as much sleep as possible, extra Vit. C (? on help it provides but Linus Pauling promoted it so who am I to ignore his advice), healthy foods, etc.
After 20 years of long haul flights never had a major problem. Lucky me!!!