For supplements I recommend vitacost.com. Their own brand is often the best value anywhere, IMO. And every month they do a sale with buy-one-get-one free or half-off. Here is my list (consult your doctor).
Basics for everyday health: Optimized B Complex, sublingual B12, Advanced C, liquid D or mini gels, omega 3 gels or liquid fish oil, Magnesium Ultra, Probiotic 15-35, digestive enzymes.
Additional options, and for flu season: zinc, selenium, Lugol's Iodine, Mushroom Complex, chlorella or spirulina, glutathione, NAC.
Try not to depend entirely on pills though - eat natural healing foods and herbs every day: organic or fresh local eggs, fresh whole garlic (unpeeled unprocessed unbottled), fresh ginger root, red onions, lemons, organic berries fruits & veg, apple cider vinegar with the mother, bone broth, raw pecans cashews and walnuts, whole milk organic yogurt, kombucha, coconut oil, fresh organic cilantro and oregeno, flax seed, hemp hearts, steel cut oats, dark kidney beans, wild caught salmon, herbal teas, etc.
About water, I would rather have a water filter system or two. Instead of trying to stockpile months worth of bottled water (which is usually just "municipal" water anyway). Maybe a manual gravity-fed filter like British Berkfield or Alexapure, plus one countertop model that connects to the faucet and uses 1, 2, or 3 standard 10 x 2.5 filters (Example- waterfilters.net/qmp603-two-stage-countertop-filter-system.html)