I'm going to be a bit of a contrarian here. I find that drinking enough water and getting enough sleep tend to do it for me. If I remember to get some extra vitamin C, I will.
I don't use wipes or hand sanitizer, just based on the idea that exposing myself to those germs keeps my immune system tuned up. I have exactly *zero* proof that this works, nor do I claim any, but it has worked for me.