I love this thread. This is something I think about a lot - mostly in the back of my head, but still.
I think that growing and producing all of your own food is something that might not be completely necessary in today's day and age BUT is an important skill or something to be set up for. I'll never want to go without chocolate, coffee, watermelon, and many other foods that I really just can't efficiently produce where I'm at, but at the same time I think there's huge value in producing enough so that if needed, you could feed yourself without getting too bored of the same two foods over and over.
Now - most of what I eat is meat. I eat about 90% meat & animal foods at the moment, with mostly nonstarchy veg and occasional treats being most of the rest. I'm actually surprised I haven't heard more people talking about the meat here. Because as I adapt to my meat-heavy diet (for health reasons, and I don't think I'll always eat this much) I've come to realize that depending on your land, meat may actually be a fairly good ROI food to produce.
For example, I have brushy woods, 20 acres of it. This is ideal forage for goats and I could very easily forage meat goats all summer and "harvest" them in the fall or early winter, with little work and extra "inputs" on my part other than the fencing and rotation. I could cut the brush and dry it for winter food as "Tree hay." Calorie for calorie, that would be a very efficient use of my time and energy. Granted, to be sustainable you'd have to keep some of them over the winter and there would be work involved to feed them, but I think it would be more efficient to do that than a lot of vegetable crops.
I figured out that between meat rabbits and their amazing feed-to-meat conversion ratio, goats I could forage, and POSSIBLY pigs for the additional fat I'd need, it may actually be more efficient food-wise to raise them rather than trying to get all my calories out of plant foods that I grow and hunted meat. This is all conjecture, though, because I have no idea how much work it would end up being to actually grow/produce/harvest food for these animals in the off-season. Someone who had a lot of nice grassy pasture (I do not) would probably do well with grazers like beef or sheep, especially the hardier breeds that might be able to get more calories out of winter forage.
The other thing about animal foods is that they are able to glean calories from foods that would take a lot more processing on our part, or they can even sometimes harvest their own. Like if you turned out pigs in an acre of sunchokes or a wood full of oaks (acorns). Or setting up rotational pastures with perennial foods that they can harvest and glean themselves. I accidentally might have discovered that the deer in this area don't readily eat a certain type of sorghum which will grow without irrigation, so I'll test grow some next year to see but that's the sort of thing you could grow, cut the stalks, and toss them whole to the chickens.
Other than that, I do want to echo the other posters who stated that this is very much a gradual, work in process where you gradually adapt HOW you eat. Learning to eat seasonally, focusing on producing all of your own of fewer crops to start with - looking at the proverbial low-hanging-fruit and getting in the swing of producing all of your own of something, while you gradually add more and more to the table. If that makes sense. Doing what's efficient.
Like starting with the things that grow in your garden that maybe grow a lot easier with less work... or perhaps the things you like to grow more. This is kinda the phase where I'm at. I actually don't even have a production garden yet - I JUST got the deer fenced out a few months ago so am hoping to get some done next year... but what my plan is, is that next year will be the experimental year where I test out to see what grows easily here with the least amount of work and the kinds of things that I (and specifically my kids as well) enjoy growing and eating. That will be the starting point.
And - at the same time as we're adapting and learning and setting up systems in our gardens to grow more food, we're also adapting how we eat, and what we eat when, to closer align with what we could produce ourselves.