There is a difference between sustainable, non-sustainable, and catastrophically unsustainable; and it’s an important difference. Having a locavore diet is very easy where I live, except for vitamin B12 supplements which are not locally sourced or made. I don’t know what you mean by “survive the winter”, it’s not an issue where I live. I only use salt and turmeric when I prepare food - tho some processed food I buy contains other spices.