the advantage of fast-food over groceries, is that you don't have to worry about spoilage and waste. So the delta is probably less than you think. Now granted McD is an s-show, they are no longer the restaurant of the poor, You likely can get a better burger meal deal at a Chilis than a McD, as sad as that is.
Good grief .. you're serious?
Flour comes in sacks, meat comes in cuts - we've a quarter lamb in the freezer, part of that in the fridge, and yeast and flour enough for bread for the next six months.
We shop cheap, like the family has done for the past 100+ years, much of our food comes from the garden - our excess gets swapped with others excess (we have a lot of fruit, we never buy eggs, they come from people that can be bothered to run chickens).
It's a bit of work, we save money by not going to a gym and our life expectancy and cancer survival rates are much better than, say, middle north America.
To cut mbfg a bit of slack here, your approach doesn't work in all situations. I admire your functioning community and supportive family and the fact that you've got time and space for things like gardening.
If people can't live like you do, it's probably because they've been placed on some kind of economic hamster wheel, and rather than figure out how to get a quarter of a lamb their better bet is to emigrate or to disrupt the system that's making McDonalds feel like a relevant factor in a survival equation by building the kind of community that you're describing. That's a big ask if you've never been part of such a thing (I know I haven't).
Sure, we live in an isolated area and have evolved through years of not even having a shop (well, I got to see one finally ~ 1980 or so). My father as young pre-teen helped support three younger siblings and a mother while his father was away at war by trapping rabbits and all that.
I had eighteen months as an isolated single parent with near zero support (long story) and had to stretch a marginal budget during that period. I've also travelled through the more remote parts of more than half of the 190+ countries across the planet, sorting logistics for food, fuel, et al along the way.
What I can pass on as hard earned lessons are that fast foods are rarely the cheapest or heathiest in the long term - if you can track down a large volume slow cooker in any garage sale or op shop on special you can keep a never ending stew on the roll by throwing in damn near anything, potatoes, celery, beans, carrots, bits of meat, swedes, etc.
It's hard to disrupt a system, difficult to break patterns and build communities and establish areas to grow food - but home cooking and stretching out food is something that can be found across the planet in the most unlikely places. Worth the effort to look for examples and make a few moves.
We're lucky to buy and prep all our food in bulk - it's more expensive on the infrequent shopping days, it's substantially cheaper over the course of year.
It's not something we need to do in current circumstances, it's a habit kept up in case it's ever needed and being frugal where possible means more to spend elsewhere.
This is just wrong. Beans and rice are more than an order of magnitude cheaper than McDonald's per calorie and they're non-perishable. Combine that with whatever fruit and veg is affordable fresh or frozen, a bit of cheap seasoning, and you're still coming out ahead.
You obviously need access to cooking and storage facilities to eat like this, but the target audience of McDonald's is the time-poor, the resource-constrained, or the depressed and disabled, rather than just the money-poor.
Even if you waste half your groceries its still cheaper than eating out. And wasting that much is difficult to do, most staples will last weeks to years without risk of spoilage.
There are some fresh fruits and vegetables that are exceptions because they dont take well to refrigeration or freezing but really not much.