Pick a month that you normally don't spend very much. If February is a month you stock up then that is NOT the month you should choose. I could choose January because most sales in the stores are for household things, "white sales" and I don't need any of those things.
I could also pick July. It is so hot we don't go out and do much, we can't afford to go somewhere cooler, we eat a lot of sandwiches and stuff because it's just too hot to turn on the stove or oven.
October is a long month to me and although we don't buy a lot of stuff that is not needed we do end up with 5 weeks in it almost every year, pertaining to pay days, it often has 3 paydays if you get paid every other week but if you only get paid once a month there are a few extra work days that have to come out of that month. It's still 31 days but it's just different on the calendar.
I wish I could spend $45 on produce every week I only get about $40 per week to spend on my entire grocery bill. We hardly ever buy fresh produce because we have to have other foods like milk and bread. We are only a family of 2 adults and 2 elementary school kids so maybe your family is much larger...
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My favorite book pertaining to food storage is by a wonderful woman who is down to earth and has thought of just about everything I can forget about being prepared and planning ahead.
Her name is Peggy Layton and her books are totally understandable and easy to implement. My favorite that really helped me start understanding what foods we use and what I needed to have on hand was:
Emergency Food Storage & Survival Handbook
http://peggylayton.net/index.php?app=ccp0&ns=prodshow...
In this book she has lists of foods and you can print them off and keep track of what foods your family consumes each month. Then you can plan your shopping lists to include these foods whenever you see them on sale so you can save money in the long run. Since you do so much food storage already it might not be something you could learn anything more from but her storage areas and basement are like going to a grocery store. She has a years food supply in hand at any time.
A lot of my friends do food storage and when there is an emergency they always come to the rescue to those who are without food. So many of my friends have donated a lot of their food storage each and every time tornado's and other natural disasters have occurred and they just emptied out their stored food to help the hungry people.