One of the biggest problems with trying to eat cheaply is to make sure that you are eating nutritious foods. My secret weapon is oatmeal. Not the flavored crap sold in little packets! You want the type of oatmeal that comes in large flakes and that takes a long time to cook. It is possible that your local supermarket won’t even carry it.
Personally, I go to the nearby health food store for my oatmeal. I get large flake rolled oats. You can also find steel cut oats in some stores. Either way, you are buying food that hasn’t had a lot of processing. Oats, when unprocessed like this, are very good for you.
When money is scarce, a bag of quality oatmeal costs under $2 and will last for a week or two. You can have it for breakfast every day with a bit of milk or yogurt. I don’t even bother to cook my oatmeal, just mixing it with yogurt or putting in some milk. If you find a cheaper meal which has the same level of convenience, while being healthy, please let me know.
It may be obvious, but canned food is generally loaded with salt, sugar and other useless ingredients while at the same time containing highly processed food that is degraded nutritionally. If you are having to be frugal then you should put a bit more time into your own food preparation, so that you can eat better and eat cheaper. For example, buy very large bags of beans and rice. You won’t find wholesome food any cheaper than this.
Finally, there is a concept out there that will generally apply to the foods you purchase. The more processed the food is and the more convenient it is, the more likely it is to be expensive with respect to its nutritional value. Oatmeal is a fantastic exception because while it is as convenient as a box of cereal and has a long shelf life it is unprocessed, healthy and almost as cheap as dirt.