Start out by putting away 30 days worth of supplies. Then extend it incrementally until you meet your time goal. Absolute bare minimium would be 25lbs of white rice, 5 pounds of beans, 45 gallon of water, multi-vitamins, something to cook it with fuel for each person per month. Add support items as you see fit like water purification, medkit, solar battery charger plus batteries, radio, toilet paper, trash bags, lighting, etc... Add comfort items as you see fit, like sugar, coffee, spices, sauces, canned goods, trash bags, booze, etc... I am sure that I have missed some essentials, but there is a lot of info on the web with what you need, but always do essentials first. Also try doing it for a day or more to determine what you are missing or need to make it livable for you and your family. Somethings that you might also do is add backup items for some really important stuff like the means to cook your food.