I take a multi, fish oil, vitamin D, vitamin c powder mixed with water and Coq10 daily. I recently bought a "greens" powder mix to up the ante during the winter months!
Getting at least 7 hours of sleep a night is key, too.
If I start to feel unwell, I take echinacea and zinc (Zicam and lozenges). Plus, ginger and garlic (yes, I'll even eat them raw!)