I worked in grocery stores for over forty years, and learned a lot about eating cheap and never paying the full retail price for any food. The real key to doing this spending as much as you can the first time to build up a supply of the foods that you eat most often.

Then start watching the grocery adds from the local stores that are around you. Grocery adds have a cycle and pretty much stay on that cycle, for instance if a store has can vegetables on sale 3 for $1.00 one week most likely in about four to six weeks those can vegetables are going to be on sale again at 3 for $1.00

So buy enough to last until they go on sale again, and you will never have to pay the 75 cents for the same vegetables again.
The same goes for ground chuck $1.79 on sale $2.49 not on sale, large eggs .89 on sale $1.29 regular price.

The idea being, just about all food that you buy will be on sale at some point and usually it will be about a four week cycle. The same applies for sodas or snack foods.

I drink Maxwell house coffee and usually pay about $5.49 for the largest can when it is on sale so I buy two or three, when it isn't on sale it is about $6.79.

Milk freezes, so I buy three or four at 1.89 and freeze it regular price is 3.59.

You get the idea, if you have a place to store it and a freezer
you will never have to pay full price for any of your foods again.

Also monitor the adds from all the stores in your area and shop the best prices, don't be afraid to shop at all the different stores, I always take advantage of the buy one get one free adds and buy as much of the item as I can afford that the time , if I have coupons that is when I use them.

Watch the adds for a few weeks and you will see what I mean about the sale cycles if you pay attention you really can eat at a much reduced cost.