The best preventive for the flu is to take the antioxidant BHT. It works by stripping the lipid coat off of any lipid coated virus. I gave some to a friend last year that was diagnosed with Shingles on a Thursday. She was covered with sores and itching like a man on a fuzzy tree. She started taking BHT on Friday and called me on Saturday and said she was all cured and wanted to know if she could stop. Not bad considering modern medicine will tell you that Shingles last at least 1 month and that you will be in excrutiating pain. I have friends that had herpes (on their lips) all their lives and completely cured it with BHT. The literature is full of bad things about it. It is supossed to casue all kinds of cancer and liver issues. If you read the medical literature you will find that BHT, taken at 500mg to 1 gram per day has absolutely no bad side effects. The studies showing bad effects use doses like 20 to 80 grams per day. In a similar vein drinking 2 glasses of read wine is supossed to be healthy yet if you drink 20 glasses per day you are going to rot your liver. It's all about the dose.
BTW, BHT works on all lipid coated viruses. Anything with an "H" in it such as H1N7 etc. This means it will work against Bird Flue, West Nile Virus, Equine Virus, Hepres, Shingles etc. The best benefit of all though is that it increases mean life span. Oh, it only costs something like $10.00-$15.00 per year. This information is considered annecdodal becasue it is just me saying it. Get on PubMed and type "BHT" to see for yourselfs. Maybe a better search would be "BHT and lipid coated viruses" Keep in mind when reading the research to look at what dose they are using. Any of the papers shoing ill effects will have used massive doses.
One more thing, the Candadian Government ( I think their version of the U.S.'s FDA) conducted a thorough study of BHT (it's a 26 page document) and their conclusion was that there was no observed negative affects whatsoever when taken at about 1 g per day.
Once you get the flu there is nothing you can really do. Zinc only works on rhino viruses. Vitamin C at several grams per pay will not help get rid of the flu but it will help to prevent secondary infections from forming.
Monolaurin, derived from either coconut oil of Olive Leaf Extract is also supossed to work against viruses but I have not done a lot of reseach on to that to confirm it.