The need for a flu shot is a myth. The flu shot is not guaranteed to protect you from the flu. The fact is the pharma industry uses fear to push a lot of "medicines" you don't need to stay healthy.
Here's how I stay healthy during cold/flu season. I take the herb Astragalus all the way through the flu season and we also use Grapefruit Seed Extract. Both are incredibly useful. Astragalus is a natural immune system builder. GSE is a natural antibiotic/antiviral that is extremely safe.
I never get the flu, but in the event you should contract it (my son got the much feared swine flu) a dose of the anti-viral drug "Tamiflu" will knock it out very quickly. My son has had colds that were more severe than the dreaded swine flu turned out to be. Once he had the Tamiflu he was symptom free within 24 hours.
Otherwise, good hygiene and common sense. Those who overuse products like hand sanitizer tend to be more prone to illness, not less. Chronic overuse of these products depletes the natural immune system and makes you more susceptible. Good old soap and water is just fine.