I am currently working on my three-month food supply, and I found this wonderful site that makes starting a food storage plan for your family pretty simple.
They just updated this nifty tool for calculating how much your family needs for a three-month supply. All you do is enter meals/ingredients for one month of meals, and the excel spreadsheet that they have created tallies up the totals and creates a shopping list for you. It's very efficient.
And if you are interested in building a one-year supply of food for your family within one year, you might want to sign up for their email check-list that keeps you on track to reach that goal.
The church also has a website dedicated to helping people meet their goals of self-sufficiency. It's www.providentliving.org