I answered a question yesterday on what two plants I would plant in my garden if I could only plant two. My choice was potatoes and sweet potatoes. It might seem like a really weird answer given all the knowledge of two nutritious vegetables such as tomatoes and kale are. They are also very delicious. However the are not very calorie and weight efficient crops. Of course, I am not taking about a garden for yummy vegetables but crops that can offer the total calories for a humans. It would likely lead to some nutrients deficiencies. No single vegetable or legume has all nine essential amino acids. Most will also experience appetite fatigue from eating the same every day. This is the reason I belive Americans weighted less before. We just did not have the choices we have now which helps us overeat.
It takes 15.7 100 sq ft. beds of potatoes to produce the 2,400 calories per day needed for the average person. That is 1,600 square feet of growing space or 1/4 acre. I would think a lot of people do not have this much space. Still in some place if people worked together or found empty land to use they could grow their own.
I have enough land to grow my own and I am working on getting up to 8,000 sq feet or 80 beds for two people and 2,400 calories per day. In these beds I will grow 60% carbon and calorie crops (e.g., grains) This would amount to 40 beds. 30% would be high-calorie root crops (e.g., potatoes for maximum calories. This would be 24 beds. The remaining 10% will be vegetable crops (e.g. tomatoes, kale ) for vitamins and minerals. This would be 8 beds. I have not got even close to that amount but I am still getting practice growing different crops so if the time came and I had needed to grow enough to survive I would knowledge plus experience.