I live in a hurricane-prone area. The rule they always remind us of right before a storm hits is "enough food and water to survive 72 hours on your own." After that, most of the time power is back on. A couple of years ago, when the main transmission tower fell in the river and the entire city was out of power for two weeks, Red Cross and FEMA were here right at the 72 hour mark passing out rations and bottled water. So we always try to have at least 3 days of nonperishable food and water on hand. Occasionally we'll pick up a few things right before a storm hits, but it's generally not necessary.