1. Buy and use foods that have high value per dollar -- peanuts, eggs, frozen chicken, canned tuna.
Grocery stores sell certain items below their cost ("loss leaders"
: milk, bananas, Costco rotisserie chicken ($5 cooked), generic or store branded bread
2. Use your freezer -- frozen fruit, veg, frozen BLSL chicken, fish, juice concentrate. All cheaper than fresh and they won't spoil before your use them.
2a. Keep your bread in the fridge. Inhibits mold
3. Buy a bottle spat and use it to get the last ketchup, etc out of those squeeze bottles
4. Cook in batches then store in servings. Chili, beef stew, quiche, minestrone, etc are great staples that can be made more efficient and cost effective by cooking in multiserving batches. There is a cost (and time) that comes from heating, reheating, washing various containers and cookware but all of that can be reduced. Store your servings in glass pyrex that matches the servings size you use. 8 oz for single, 16 oz for a couple. You can reheat directly in the glass. Also avoids some microplastics.
Cook "blank" so that you can use something as the base for a variety of meals. For example if you cook chicken in just its own juice and salt it can become chicken salad, tacos, pizza topping, stir fry, etc. You can get cook in bulk but still retain options for variety during the week.
5. Switch from soda to tea. Tea is 15-cents per serving. Use real sugar if you like that and avoid HFCS.
6. Jarred red peppers. Preskinned, preseeded. Much cheaper than the ones in the produce dept.