Summary: it is agriculture that will undergo the most important revolution, never leave the land uncovered, as in the forest. Use of permaculture in all areas. Low technology and low energy mandatory from the beginning. Many relationships with farmers
It is based on a science developed since a few decades to harmoniously live men and nature:
Permaculture. It's not just an agricultural technique. It is a way of life that takes into account the essential relationships between men, between men and animals and between people and nature, and it is not only ecology. I see on some site yet eminently interesting solutions for making wood stoves with two car rims (yes, they will not run much for lack of fuel.) If such solutions spread after the collapse, in less than three years France will be transformed into a plant desert.
You can read a description of the twelve essential rules in this site.
Agricultural production is based on mounds in living soil. This technique has three essential advantages:
Very little water needed during cultivation
Very little gardening work
A very large production (about ten times higher than gardening).
Rearing of farmyard animals contributes to the production of vegetables by providing phosphates, phosphorus and natural fertilizers
The orchard is also treated with special rules. The density of trees is much greater than in traditional techniques.
Tree feet are occupied by several strata of vegetables and bushes that significantly increase productivity.
Finally, relations with farmers enable them to produce indispensable elements such as wheat for bakery and pastries, corn for animal feed, milk for butter, cheese and cooking, etc.
No longer having energy, they will be happy to find on the farms organizations that allow them to have the labor for field work and to give them the food they can hardly produce in their fields.
Farmers will therefore be full members of farms and estates even though they will hardly be involved in farm work.
Other activities will quickly become important as horse breeding. Indeed, if it is possible to travel by bicycle, a lot of transport and including the transport of people will be done with the help of horses. This activity should be analyzed well before the collapse and certainly implemented because it takes a certain time to produce animals capable of working.
Many other areas will have to be analyzed such as the production of fabrics, leather for shoes, salt for the kitchen, etc ...