Agreed, you can't be self-sufficient! But you can save a ton of money by gardening! This was my job for ten years - I worked in schools, food banks, and food pantries, teaching people how to grow food inexpensively and get the most bang for their buck.
Buy the cheap stuff - like grains, starchy tubers, and legumes - and grow the expensive stuff, for example:
herbs (mint family always in pots, never in the ground)
garlic, shallots, green onions
ginger (in pots, overwinter indoors)
lettuce, spinach, chard, arugula, kale, and other greens
tomatoes, peppers, eggplant
strawberries, blueberries, blackberries, raspberries
tree fruit and nuts (if you have room and time for an orchard)
Even living in an apartment and growing in windows/balcony, I saved maybe 25% of my June-November food budget. Now in a house, with mature fruit trees, eight raised beds, bees, and chickens, I save maybe 50% from June-November and 20% the rest of the year. And meals are way tastier and more nutritious!
(Funny side note: no one I know has bought peppers, hot sauce, or spicy seasonings in years, thanks to what my housemates call my "capsaicin garden" - one whole bed of habaneros and scorpion peppers. Have to cut the grass around that bed by hand b/c if you run the mower over it there's a good chance you'll turn a few fallen peppers into DIY pepper spray.)