Historically most farmers were engaged in these practices for subsistence, and this is still the case in the poorest developing nations, where over one billion people live on under one US dollar per day, and two more billion live on under five dollars a day. To half the human population on Earth, money is a minor consideration in how agriculture works, what crops are planted, and what tools and methods are used. Each region has a few traditional crops, and methods to grow those that amount to gardening on a large enough scale to feed one family or extended family.
Cash crops are never the motive of subsistence agriculture, rare foodstuffs can be gathered in the wild and sold there. The bushmeat trade is such a sideline — hunting of wild animals to feed the cities.
The Peruvian economist Hernando de Soto has argued that one obstacle to industrial development is that subsistence farmers can not convert their work into capital which can be used to start new businesses and trigger industrializations. He argues that these obstacles exist often because subsistence farmers to not have clear title to the land which they work and to the crops which they produce.