How can I keep myself from catching it?

My aunt had the "flu". She ped it to my mom, dad, and cousin....so it's definately contagious. I DO NOT want to end up hunched over the toilet anytime soon. What can I do to nip it in the bud...and keep it from getting me sick? I've been drinking lots of water. We have no oj, but I ate a can of mandarin oranges. What elsse can I do? I have a fairly weak immune system...