As I said elsewhere, make sure you can share knowledge and work with other survivors. A community of people with various skills (even if you give them the book and they learn it) makes survival a lot easier. Maybe your garden fails, but if you have a few other people you work with you can support each other and everybody lives.
It feels like you're suggesting prepping for a Shit Hits the Fan type scenario, which the OP post explicitly says is unreasonable. It postulates a world where most people would starve because growing plants to survive through a year is extremely difficult if you don't have any experience doing it, assuming you have enough land time and other resources to even do it properly. And I guess I just doubt that a box of seeds and a willingness to share your garden would see you through the year. You would need a whole lot of luck.
Major metropolitan areas devolved over centuries from how I understand history (I'm not an expert). that means you and your descendants have time to figure it out. However where to go is a question. My [very limited] plan is since I live in Iowa, I'll just find a farmer who can't get fuel for his tractors and thus can't afford to farm his land anyway - I'll buy a small homestead cheap and make it work. I have a few books from 1920 on how to do things that might be useful, but I suspect the local library has others. However if you live in New York you will find all the land taken by the time you can walk to Iowa...
There is also the case where war killed everybody in the city, but that isn't devolve and I'll ignore it: prepping for an afterlife is a religious discussion. I feel the need to acknowledge this though just in case.
Overall though, I don't think this is a realistic thing. I haven't done much more prepping than the above. Civilization won't collapse - and even if it did I'd probably die in the collapse so I'm focusing my preparing on religion which applies even if civilization doesn't collapse.