>Anonymous, sure. But how can anyone be self sufficient in a city?

Glad you asked! Let's go over your questions.

>Do you have a large garden? Rainwater tanks?

I've got space on my roofs for a garden - I own a three story building that has 100% lot coverage (something you can still afford to buy in Philadelphia) I could easily install rainwater tanks indoors (since our rainspouts travel inside our house to drain into the sewer line) or outdoors - but I walk to the produce merchant and use one of the longest-operating municipal water supplies in the country. Currently we just have herbs and cherry tomatoes in our roof garden.

>The tools and workspace to do your own plumbing, construction?

As a matter of fact yes. This is the third home I've owned. First one was built in 1905 in the suburbs and was a gut job. Everyone should have a circular saw and an 18v cordless drill, but I've also got plumbing supplies and electrical supplies. We hired contractors for this place because it was a complete gut job (down to three walls, and we had to install steel structure) but we generally don't have to call contractors unless we're short on time. Our second house was built in the 90s and didn't need much work, but since we learned on our first house, we updated the floors (we have tools for tiling too) and cabinets - largely pre-built. We tried something more raw on the first home, and it nearly caused my wife and I to divorce. Why bother when mass manufacture has solved the problem? Even still, I do tend to build my own desks/shelves.

And, being in a city designed for horses, if I'm missing tools, I walk to the hardware store. I've got a van, if I need bigger things than I can carry. And if I didn't have a van, I could take transit (or a taxi or rideshare) to the big box store, rent a truck from Home Depot, and use that to transport big goods.

>Do you have solar panels and batteries?

I've got a long flat roof, and a neighbor who sells solar. We've opted instead for a green roof, but that's sort of a phase three thing for the building. Talking about self-sufficiency while ignoring the benefits of society, then simultaneously crowing about solar panels seems a little bit like moving the goalposts in terms of what counts as self-sufficient.

>If the utilities all shut down and the grocery stores all closed, everyone in a city would die or flee.

That's a big if for a city, but a reality in rural communities. In my lifetime, towns in my country have been abandoned. WalMart moves in, and Main Street is boarded up in a matter of years. Industry gets offshored, and people who can afford to will flee. "Ghost towns" are an attraction across America.

The closest thing to a ghost city in my country was Detroit in the early 2000s. Even cities destroyed in wars are rebuilt more often than they aren't.

>It is impossible to be self-sufficient in a city.

Context matters. If you want to talk about bronze age self-sufficiency, I'm sure it's a great thought experiment. There's an efficiency modifier to self-sufficiency in urban environments, and as evidenced by placed occupied for multiple millennia such as London, Constantinople, Beijing, or even cities like Berlin and Baghdad and Cairo, even when things get real bad, cities are much more likely to recover.