Foremost.....stop buying commercially prepared foods. That means just about everything in the supermarkets. We gradually transitioned to producing or trading for most of our food. At the same time we weaned ourselves away from most store bought items. But lets say that we weren't growing our own, would it still be possible to do? Sure. We would have needed to adjust our diet and purchase just "real food", things that are zero processed with zero additives. I'd look to buy direct from the grower when possible. I'd check out farmers markest. I'd look into bulk buying or a co-op.
Next......stop eating out. Or at least drastically reduce it. We are down to two "out-with-friends" meals a week, one a breakfast, the other a dinner. While we could survive just fine cutting these out, we have no plans to. Eating a meal with friends is very important to us and very enjoyable.
Stop buying at expensive stores.....those little convenience stores can be pricy. And there is a big variation in cost between different supermarket chains.
Stop wasting food....this is another super biggie for me. I learned to use food that previously I had thrown away. It was hard but I've retrained myself not to leave food go bad in the refrigerator. I've switched to making stir fries, soups, and stews which can use up leftovers. I've learned to freeze or dry my excess. I don't bother to can foods, but that would be another option. During the hectic chapters of my past life, I was immensely guilty of wasting food. Alas, no more. Different lifestyle, different focus.
Establish a trading network..... these past few years I've created a trading network to turn my excess foods that I produce or acquire into other foods that I want. I have traded for meats, milk, cheese, fruits, veggies, bread, cookies, pies, and even ducks, lambs, chickens. I'm often offered jams, jellies, syrups, dried fruits & veggies, juices, and assorted homemade foods. Last week I traded for some homemade fried chicken that was absolutely lay fantastic.
I've never kept the records, but I bet I spend a helluva lot less now on food as compared to when I first moved here. Looking back, it was insane how I spent the food budget. Heck, what budget? I just bought food as wanted. And back then I was really habituated to commercial foods. Microwaved food was my thing. No more.
If I were just growing a small food garden and not doing all the other stuff, like trying for a complete food line, foraging, and trading, I think I'd focus on growing those veggies that are expensive to buy in the stores. Things like sugar snap peas, snow peas, cherry tomatoes, asparagus, etc. Growing those pricey veggies (and fruits) myself would help the food budget. But of course that would mean growing them sensibly. One wouldn't save any money if one were to spend big bucks on fertilizer, pots, potting soil, hand tools, a rototiller, etc.