I'm trying to plan for a 6 month to a year supply cutoff but due to job layoff not a major earth change as I work in IT so a job layoff is a realistic possibility. I've started by trying to make sure I have anything non-perishable items such as paper plates and silverware so I could cut down on water used for washing dishes. Buying food in bulk like rice will not help for 6 months because after eating it every day for a month you will be sick of it <img src="/images/graemlins/smile.gif" alt="" />. Start by printing an empty calendar and put it somewhere in your kitchen, then as you eat each meal, write it down. This helps in two ways, one you can look back and make sure you didn't eat the same meal just 5 days ago, .i.e. start to give variety in meals so you don't get tired of something. With just my wife and I in the house it gets difficult just to think of enough meals to go a couple weeks without repeating or getting tired of something. Take the filled up calendar and sit down and look at the meals and see what can keep and for how long. Estimate how much of each thing you need then, for example if you eat green beans average of three times a month then you know you probably need 18-20 cans of green beans to make it those 6 months. There will be meals on that calendar that consist of items that won't last 6 months so you know if something were to happen you then know what to finish up first and what can be left for later and what will have to be eliminated. If you get to the point where you can actually keep a few months worth of food in stock during normal times then you can actually think about having a supply for a scenario.
The hard part is 6 months of water, 1 gallon per person per day is 182 gallons of water per person for 6 months. Better start buying those quart bottles of water now <img src="/images/graemlins/smile.gif" alt="" />