I dont do anything really and I have a compromised immune system from asthma and immunosuppresetn drugs and i amazingly rarely get sick.
I dont cut anything out of my diet completely. Ive talked to my nutritionist about that many times and she always tells me as long as I eat a diet that is mostly healthy (fruits, veggies, water, grilled lean meats, fish, etc) that having soda, occasional fried foods adn sweets is no big deal at all.
Even drinking 1 soda/day Ive lost 45 of the 60lbs i gained from 3 years of prednisone.
So basically, I eat a balanced diet (with some treats thrown in here and there), and do 10 minutes of aerobic (all im allowed to do) and 35 minutes of non aerobic exercise at least 5 days/week. I dont use hand sanitizer, I dont take vitamins or supplements or any of that stuff.
The only time I am at the doctors is for routine checkups pertaining to my asthma, arrythmia and allergies unless its for an asthma flare. I dont get colds, i dont get the flu (knock on wood), etc.