I've been there too. Buy ingredients, they're cheaper than the end product. By that I mean flour, sugar, milk, eggs, butter. You can make many things with those and much cheaper than you can buy eg biscuits, cake etc
I like making little herb and cheese dumplings (flour, milk, butter, dried herbs) to go on mince bulked out with grated root vegetables. Really yum and filling.
You can get 1 kg of flour in Australia for $1.25 - you get 8 cups to a kg - so 15c a cup, which is cheap.
We have fruit and vege ships here. Some are really cheap and have big bins for sweet potato, pumpkin etc at prices a fraction of supermarket prices. I also found eggs, milk and bread cheaper at these. One near me now is stocking tins of tomato etc at low prices.
If you have the room for a vegetable patch, a cost effective approach is to reuse the seeds from things you buy. Mum used to keep the seeds from nice pumpkins and put them in the vege patch. You can do that with lots of fruit and vege - google for tips.
In really bad times, my go to was egg on toast, jam and toast. Bread here can be cheap if you know where to look. If I could afford milk, then I'd do french toast. Work at the time provided vita weats in the snack room, so vita weat and vegemite for lunch.