Using coupons is one way that you can build up your 3-month supply, it's not for everyone but if you are interested you might want to check out these Q & A posts from one of my favorite coupon sites. It's called A Thrifty Mom.
Q & A Start Slow
Q & A How to Start a Healthy Stockpile
Extreme Couponing the right way
Q & A Start Slow
Q & A How to Start a Healthy Stockpile
Extreme Couponing the right way