Watch for seasonal sales. Here in the US somethings are always on sale at certain times of year.
I get winter squashes in October store them in my basement and eat them all winter. Butternut Squash is my favorite to stock up on.
Other examples include frozen turkeys in November, baking supplies in December, cabbage in mid March, eggs around Easter and so on.
Other stuff goes on cyclical sales and if you track prices you can buy at the low points.
I prefer to get cuts of meat with the bone in. That way I have a steady supply of bones for bone broth. I use bone broths in my cooking all the time. It is great for slow cooking of tougher cuts of meat, soups, gravy, and cooking rice in. It add a lot of flavor for very little additional cost. I put the bones in the freezer till I have enough to make a large batch. I pressure can or freeze it in meal sized portions.
Save the fat! I save the bacon fat and other animal fats from cooking to use later. This is amazing stuff if you can get it from pasture raised animals. It saves me money, I use a little more of the animal and I need less, butter and coconut oil.
Grow sprouts herbs, and baby greens indoors. I do this in the winter when the garden is frozen solid and covered in snow. Sprouts are surprisingly easy to grow and can be done in the smallest of apartments. I already have seedling trays, potting mix ,lights and shelving for growing seedlings so growing baby greens in the off season is easy. I will also grow sunflower shoots for my laying hens. Potted herbs are an easy one to grow and use. I cringe at the price of "fresh" herbs in the stores.
Buy whole spices in bulk and grind your own seasoning mixes as needed. So many spices overlap in seasoning mixes that you can buy the whole seed of a fairly short list and be able to add easy to grow herbs to create most meals. I buy peppercorns, nutmeg, cinnamon, cardamon, cumin, coriander, mustard seeds, dill, celery, cloves, allspice, anise all in seed from small specialty stores or order online in bulk. This selection with a bunch of dried hot peppers and a growing assortment of culinary herbs from my garden makes low cost foods taste amazing. I use an inexpensive coffee grinder or a mortar and pestle to grind what I need. This saves money, whole spices keep longer, and saves precious space in my small kitchen.
I batch cook and left overs are always divided up into serving sizes and frozen. This saves time and keeps us in easy heat and eat meals when we are busy or I am not feeling well.
Learning to can, dehydrate, blanch, freeze, and ferment foods also allows you to take advantage of good sales, free produce from from people you know, and foraged foods. I canned 6 quarts of pear pie filling from pears a friend gave us. I also have 3 gallons of autumn berries in my freezer to can into pie filling and barbecue sauce. We also have wild black raspberries in my freezer to can up that we picked this summer. All of that produce was free to us other than labor.
Batch cook with your friends. When my friends and I were broke in our early to mid 20's we used to have dinner partied where you brought the ingredients for a dish to the party and we all cooked together. It was fun, low cost, and I learned so much about cooking since my fiends were from all over the US and the world.
These days one friend of mine and I will get together and batch cook something like chili, soup, or jam. We both have tiny farms and her husband hunts. We will pool our ingredients spend half a day cooking and chatting. We split the finished meals and save some money while we are at it. Meals to be cooked are decided based on who has what ingredients on what free and or low cost ingredients we each have.