I have a third of an acre lot, and this is close to how much land one person needs to survive on if using intensive planting techniques. I bought my new house in a tiny village where I'm allowed to have hens (and I looked at homes in the country, where I could have had goats, a milk cow, or raised any animal I wished), and that could add to my ability to survive without visiting a grocery store. With a patch of grain grown for the hens, and discards from the veg garden to supplement what they'd find pecking around the yard, I could keep a healthy half-dozen hens. For now, though, I'm focused on expanding the food-producing area of my yard.
I lived in Oregon's Willamette Valley once, and if you don't know of it, it's a perfect gardening locale. I had grape arbors, an apple tree, and a veg garden behind a chicken-wire fence. There were also local small farms that had inexpensive fresh produce as well and pick-your-own strawberry fields. Wild blackberry bushes were all over the place, and it was easy to get as many as you could want for no money. It was a lush, beautiful place, and it seldom froze or got over 90F there. I didn't realize how lucky I was!
In Arizona, I grew mostly tomatoes in containers, had to wrap them with netting or rabbits would eat the flowers, they were so desperate for food, and grew them from seed (plant seeds around Feb 1, water every day, harvest by May. Voila.)
Where I am now, it's a four-season place, and while with a small hoop row cover, you could harvest greens an extra four months of the year, usually May through October are the months for harvesting (or "cropping," if you're living elsewhere). I'm still fighting rabbits, not to mention the bugs that eat the brassicas, but I'm already growing a wider variety of food: tomatoes, peppers, chard, squash, and bok choi comprised my first spring planting. Next year, there will be a good deal more and seven varieties of tomatoes, not just two. Also, I learned some lessons I'll apply next year. And I've grabbed some trellises at yard sales for a dollar here and there that will help me maximize my use of space.
Right now, I'm making leaf mold and piling up various compostable items I can find on two new raised 8 x 4 beds. The idea is, over the winter, the organic bits will compost some more, and in spring I'll add a mix of top soil, peat (or equivalent), well rotted cow manure, and perhaps a bag of commercial compost to the top of each bed, plant into it, cover it with a final layer of more saved leaves from this autumn that act as both mulch and compost, and grow. Every year for the next several, as that base layer shrinks down with composting and the worms having at it, I'll add more organic material.
Here's a video that shows the sort of thing I'm talking about:
And if you want, you don't even need to build the sides of your no-dig "lasagna" bed (though that's carpentry anyone can manage--four boards, twelve screws, and done), but just do it over your grass lawn or weedy lawn and get to planting. Don't walk on it ever (so keep it fairly narrow, probably 4 feet, so you can reach to the middle), and you have a productive soil from year one that only gets better as you add to it.
One of the great things about this system is the soil is so loose, you don't need anything more than a trowel and your hands to harvest. Watch my current favorite youtube gardener, Patrick at One Yard Revolution, harvest his potatoes for soup this year.
I have a set-up for seed-starting so I can harvest earlier (I should be getting lettuce, bok choi, and spinach by the end of April, weather permitting), and keep accumulating weird containers to start seeds in. (toilet paper tubes for plants that hate to be transplanted, for instance, and I can't go to a potluck but that I'm rescuing the plastic top off the disposable cake dish). Best of all, I'm enjoying the learning, planning,and even the work a lot! Now, talk to me when it's 95 degrees F out there and I have to mow, and I'll complain all day long. But for now, I'm having a fun time, and I'm reading books like this about the science of gardening advice.
I hope to never actually need to survive off my own yard, and I'm not ever going to be willing to shoot strangers over them stealing a few potatoes, but perhaps one day I'll be in such dire financial straits I need the back yard garden in order to eat sufficient food to stay alive. The way the world is going, that doesn't seem like a silly thought any more. I'm getting the system in place, and living through my failures while I have the energy and initial cash to start it up. It's not super-pricey, mind you, but the first heirloom seeds before you begin to save them, the first tools, the bit of lumber, and a few bags of compost before your own pile is large enough to provide all you need will set you back around a dollar per every square gardening foot that first year. After that, if you save seeds, you need to spend almost nothing.
If you don't garden, you may not know what you're missing! Start small, with a 7-gallon container or grow bag for a cherry tomato plant, or new potatoes if you don't like tomatoes, and see if you don't think the small effort was worth what you'll be eating as a result.