Stored food is a good means of knowing exactly how long you and your's will be able to eat before having to resupply or begin "living off the land". Many companies sell stored food buckets with a specific number of servings and will tell you how long certain size groups of people will be able to eat with that amount stored.
A good initial plan for someone who is beginning in their preparedness is to store prepackaged long-term storage food. Two well known companies who produce this type of food are "Mountain House" and "Wise." I only have experience with Mountain House, and their quality is at the top of the industry. Many companies produce these stored food in buckets that have packaged portions and meals. You can buy these buckets and calculate the amount of meals you have per person in your household per day. It's a good idea to store enough of these to last you family or survival group for between one and three months.
Of course, you'd like to have food for long than that, so store as much as you can. Eventually your group will need to be able to find, grow, hunt and fish for food. But in the event of a short-term emergency, this prepackaged food can be a life saver. In a long-term emergency, prepackaged good can allow you to have a backup supply in case you aren't able to produce food for a short time.