In an emergency, food and water supplies can be disrupted, possibly for a long time. It makes sense to have a short and long term strategy for insuring your access to food and water in a crisis situation.
Short term Keep a supply of bottled water, and a means of water purification available. (Water purification supplies and systems can be found at Nitro-Pak through the link here.) If you have a well, make sure you have a back-up way to pump water if your electricity goes out for an extended time (e.g., a reliable generator compatible with your house pump).
Keep bulk food in a cool place in your house, and rotate through it. Rice, quinoa, and beans are good staples that can be bought in bulk and replenished as you use your supply. But many foods store well without refrigeration and can be adapted to a food-rotation strategy.
Longer term In a ‘long emergency’, to borrow James Howard Kunstler’s term, stored food and water will quickly run out. If you don’t have a well or catchment system, you will, realistically, be at the mercy of local government and emergency aid. But rainwater catchment for drinking purposes requires planning, filtration, and possibly purification. Water captured in the open air is subject to airborne bacteria, fecal contamination, and roofing chemicals/metals. Help yourself by trapping the cleanest water you can, but also filter and purify it before drinking. Water filtration equipment can be found in many stores and online; water purification supplies can be found through the Self Sufficiency website, as cited above.