Practically everybody has food for a year. Few have food for a week and less for a month. When you need food for a year you can safely assume that nobody will ever care if you break into all your neighbor's houses. Their canned soup is part of your food for a year. When you need food for a week all your neighbors are looking at the pantry at the same time and trying to figure out if they can last two weeks.

Food for a month doesn't really exist as a need. Either emergency supplies from around the world arrive in less than two weeks, and you are safe, or they don't and you need food for a year.