We don't have much spoilage at our house. Stuff gets eaten quickly. People living alone can reduce expenses by eating with friends on a rotating basis. Somebody buys a family-size package of something which the group eats.
What spoilage? I just freeze leftovers in small, 1 meal/2 serving containers. When times are really tough, I throw away nothing. Leftover salad, veggies, the water from canned veggies, any scraps the dog doesn’t eat, all go into my soup makings tub in the freezer to be added to whatever poultry carcasses I have accumulated. Usually makes 1 gallon of soup a month, usually with added rice or barley.
Just use the Green Bags for produce and when you are down to just a bit of this and that, freeze it for later use in soup or broth.
Any prepared dishes that manage to have leftovers too small for lunch or a snack, get added to the dog’s food.
If I open a can of something that might spoil before being used up, I freeze it in small containers, label them and find a use for them in the future. Family-sized packages either get broken down and frozen separately or cooked up once, then packaged for later meals and frozen. A Foodsaver is a good investment.
A lot of non-edibles like ziplocks and aluminum foil can be washed/rinsed and reused. Paper towels can be wrung out in water and reused for something non-food-surface related.
I shop and cook just like most of the posters here. Look at how many of us do this as a matter of course. At $5/day/person, that is $300-$310 for two people for a month. If I watch the specials, we also have steak once a week. We eat really well.
In my area, a couple gets $350/month in SNAP. That is a lot of food and they get it in one monthly chunk, not in one $5 bill/person/day. That makes it really easy to take advantage of bulk sales and specials.