Focus on water first. Food grade buckets to collect water from a nearby source, garbage cans for rain water, water for washing. Water filter, like a Berkey for purification. Water storage such as 55 gallon food grade barrels. If you have your own well, try to get an independent power source to run the well.
I bought a house with a pool for just this reason. My plan is to filter all water through a Brita filter. Drinking water will then be filtered again through a backpacking filter. Sound Good? Or is my plan flawed?