Cave people were self sufficient with sticks and stones, at least enough to perpetuate the species.
Sure, they dealt with high infant mortality, birthing mortality, communicable diseases, starvation, harsh conditions, etc.
Our closest primate relatives still survive in the jungle with no other tech or tools other than sticks and rocks.
What they two had in common was a large, functioning, ecosystem. Without it, there is no way.
It can be done, with tech almost anyone could understand. Everyone just needs to accept the fact that there will be bad, very bad, times, on occasion. Perhaps even frequently.
I was in my early twenties when I realized and said, “It would be easier to start over in a mud hut, than it would be to make what we have sustainable”. I don’t feel any different today.
Thanks to some pretty nice tech, we can observe how some of most primitive people in the world still live. It is spartan, on the edge at times, but amazing to witness. Sustainability/ self sufficiency looks a whole lot more like tent camping than a suburb.
With enough land (huge caveat), and willingness to accept increased hunger/mortality, I really believe a motivated group could achieve 90%+ self sufficiency.