As someone who dabbles in gardening I think it is worth mentioning that gardening and farming today is about as far from self-sufficiency as you can get. Most growers use motorized equipment to prepare the ground, herbicides to suppress weeds, soil conditioners to adjust acidity etc, they buy all their seeds from commercial farming suppliers, they use commercial fertilizer and they spray their crops with pesticides.

Try growing crops with to none of the above and you'll find it is a daunting prospect that will quickly reveal why we sometimes see people on tv starving in other countries because of crop failures. I think to have any hope of self sufficiency you probably need enough land available that you can raise cows to create fertilizer but at the very least, chickens and goats. Of course then you need a way to grow and store winter feed for them... If the world ever gets to a point where self suffiency is a must, 99.999999% of the population will have no clue how to even start so those that did learn and prepare will face hordes of thousands and millions of people marauding across the countryside tearing up everything they might be able to eat. The resulting carnage would continue for months until everything edible is consumed. All that will be left to eat is each other and don't think for one minute humans wont resort to cannibalism.