For me.....I like to know what things cost normally, what I can occasionally find them on sale for, and then with both those numbers, and the expiration dates, I make my final decisions whether or not I purchase some, none, or many.
For example.....Walmart has DAK hams at $ 3.89 per can almost all the time, with an expiration date of 2014 usually, and the other day Sam,'s had a three pack for $9.19. That means that Sam's price per can is $ 3.06. Having been watching these cans for a while, haven't seen them cheaper. So I grab a three can pack and turn it over and view it's "Best Used By" date. Sometime in 2016, so I got all of the three packs I will need for the next five years.....and done. (42 cans to be exact...the extras would be an excellent barter item )
The key was for me to 'need' some canned meat. I feel it will add fat to my diet when the deer, squirrels, and rabbits around here cannot because they are so lean- SHTF. It has a good shelf life and I actually enjoy the taste. It will go well in a pot of beans, or on a salad, etc. So a versatile food that eats well and will last for years and purchased at a significant savings- WINNER.
The green beans, corn, peas and such I rarely find deals at Sam's. I was getting plastic wrapped four packs of Green Giant brand cans at Winn-Dixie for $1+ a few weeks back, when using their savers card. The expiration dates were 2013 so- winner. Sam's typically wants to sell me that stuff for more money.
Chef Boyardee Lasagna at Sam's, bundled in an 8 can pack for $ 10+. Very tempting.....all bundled up like that. But that is what I call Sam's "Apparent" value. It isn't a real value, just looks like it would be. Because I have been obtaining those very same cans with a very respectable 2014 date on them at $10 for ten cans. Less money plus 2 more cans. If I didn't know what they were really worth I might have bought the Sam's product. So what- I eat Chef Boyardee.
So you could make a list of all the things you wished were in your stocks, and then determine what each costs normally, what you would expect to see them at when on sale, and then use that list to determine when to buy in bulk. Shopping all the stores in you area also is good. Obtain a savers card from each and look up their fliers on-line. The stores use attractive sales to get you in the door, so let them. Just make sure you only buy the sale items. LOL
To do this right, you must have a well stocked pantry. You want a well stocked pantry anyways- don't you ?
Don't go shopping when you need something because you are out, as this gets expensive. I used to go shopping that way and it was always expensive. I would wander the aisles- yeah I need that, need that, need that, and none of it was on sale. Nowadays I don't need that, don't need that, don't need that either, but at Buy One Get One ( BOGO )....... suddenly I do and will be getting eight of them thank you very much......and oh lookie here I have a coupon, too.
I leave the first store with only non-refrigerated items that were specials on sale. Hit the next store and do the same. Hit the third store and do the same but also grab some milk and meat and go home. My carts are full but the money paid is small. The people in line behind me gasp when they hear the cashier tell me how much I saved, even when I didn't even whip out my coupons. Get right with their cycles, and use coupons and you can slaughter them. That frees up money elsewhere in the budget. The prices we have today are high high high. Shopping smart is self-defense.
CouponMom.com helps me to organize my Sunday paper coupons and to know what I will get at each store. When I shop commando, half price is easy peasey pudding and pie baby. Seriously, you can push out a very heavy laden cart for surprisingly little cash. You just have to get determined to do it, keep your discipline, and use your head. The resources are readily available.
Soups are a great example for me. OK....not all soups are created equal. Let's talk Clam Chowder. Progresso's isn't as good as Campbell's in my opinion. I am the only one who eats it so my taste buds win. Why buy Progresso's when it is on sale ? Why buy Campbell's unless it is on sale. Normally $2.83 a can. On sale BOGO get 20 cans and be done. The only fly to watch out for is the expiration dates. Something that will not last is not a deal- get just a few. Maybe another store is also having that soup on sale....hmmmmm maybe their dates are better. You have to work at it. Often times multiple stores offer the same item at the same time. Most sales allow you a few days to re-visit, but once you bought it you are done.
I have taught several people how to shop like I do, and they love it. It doesn't require a great deal of effort or large three ring binders full of coupons, or extreme anything. I might go full extreme later, but for now I enjoy saving 30-70% off my grocery bill the easy way. I have already had to expand my pantry because I did so well. Feels good and I almost never
have to go grocery shopping anymore.
So in review......know your product's normal market value, what you could expect it to cost when on sale, what it's shelf life would be normally, then be patient and wait for it to go on sale big time, then stock up and load up, and you are now done and don't need to buy anymore. Change your style. Learn a method that utilizes coupons, and use them when things are already on sale.

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Shop all the stores in the area....obtain their savers cards and let them email you their fliers for the week and specials. Make a list that has you going into this store and getting these specific items, then this store for these items. Don't get anything that isn't on the list....PERIOD. Don't budget your grocery expenses.....lower them by using knowledge. Then you just cherry pick stuff, on your terms.
Remember.....sometimes things seem to be a bargain when they are not. Just because the grocer lists something "2 for $3" doesn't make it a bargain. Normal price might be $1.59. LOL. Just because something is packaged in bulk doesn't make it a bargain either. They try to trick you visually, it is important that you know what something costs.
BOGO is usually a deal and they are popular right now. But usually only about a dozen items in each store will be BOGO. If it is something that you normally would eat, and it has a good date, and you almost never see it any cheaper, and you know that the store down the street doesn't have a better deal, get you some in quantity son, and then whip out that coupon and finish them. Stock it away. Laugh when you don't have to go to the store next week to get more of it. Kill three birds with half a rock. Spend your savings elsewhere, and after you get on top of your pantry, and it is packed full, you will see that things start to get really really cheap and you don't have to go shopping near as often as you used to. Then help others with what you learned along the way.