1. Start by making a list of the food you normally eat and items you regularly use. Over the next week tack these items on an excel spread sheet. If you take these items and multiply them by 14 to be safe. (14 weeks just in case there are 5 weeks in a month) You will have a good idea of what you will need for your family to survive for 3 months.
2. Gradually purchase the foods you normally eat in bulk as they go on sale. Try combining sale prices with coupons for even more savings as you stock up.
3. Use and rotate these foods in all your daily cooking.
a. Constantly replenish the stocks of these foods as they go on sale again.
b. Don't forget to include non-food items in this step as well. Get a 3 month supply of NECESSITIES such as diapers, medications, toilet paper, toiletries, etc.