There are certain things at the grocery store that are always on sale. In Korea, there tends to be buy 1, get 1 free sales on things like cooking oil, breakfast cereal and other processed food and toiletries every month or so. A way to take advantage of these sales is by never getting into the “desperation” phase.
When I notice something is getting kind of low, for example a half bottle of oil or 10 rolls of toilet paper, I’ll add it to my list, which is just a page in a simple notebook I keep on my kitchen table. Then, next time I’m at the grocery store, I’ll check and see if it’s on sale and if it is, I’ll buy 2. The one I pay for and then the one I get for free. If it’s something that I use a lot, but rarely goes on sale, I might even get 4 of them. If it’s not on sale, I’ll just hold out until the next time, or the time after that when it is on sale and when I get home, I’ll add it to my list again for the next time I go shopping. But, this definitely requires organization and a critical eye to notice when things are only a little low, but not at the critical phase yet. It also requires some money in reserve in order to buy bigger quantities of things that you might not immediately need; it probably wouldn’t work that well for someone living paycheck to paycheck.