No one can tell you how you should prepare for a disaster, because all of us have different situations we must take into account. The important thing is that you assess your threats, and determine how you can prepare for them if they occur. You need to do what you feel is necessary. If you feel comfortable knowing that a week's worth of food and water is stocked up in your kitchen, you're prepared. If you buy a house in Florida to fly off to, you're prepared.
Many survivalists pick the worst possible scenario to prepare for.
Others choose to prepare for moderate occurrences of their risk situations. Often times, preparing for the worst involves a lot of time and money. As with all other aspects of survivalism, to what level each individual prepares is up to them. I may feel comfortable with a weeks supply of food on hand, you may want enough for a month. Or a year.