Jen,
I also try to avoid the things that sound like quack supplements. I just take a multivitamin and 500 mg of Vitamin C daily and haven't had even a head cold in probably at least a decade.
For me, diet is very important, as Gary said -- lots of fresh fruits and vegetables, whole grains, quite a bit of fish, and very little red meat.
In the years since my treatment ended, I've been able to travel to some third-world countries and had no problems with local food or travel conditions as long as I observed basic hygiene steps, like frequent hand-washing.
I still see my medical oncologist every 6 months (just saw him yesterday, in fact) and he regularly monitors my blood counts -- so far, so good.
I guess what I'm saying is hopefully you'll find that it gets better for you with a bit more time, and you won't feel quite so restricted in what you can do.
Cathy