Basic engineering and machine maintenance. A thorough understanding of how leverage, gears, and pulleys work. Animal husbandry. Different ways to generate power. Basic physics and chemistry.

Yep. The more you know about how things work and what materials make-up things that will be left behind, the better your chances to make it long term.

Of course, keeping in mind that modern life isn't going to disappear over night. But, you might be without power or supplies for a long time.

There's also the idea that the more of us who can and will get off the fossil fuel teat, the quicker we can force our society to change before big business and capitalism kills us all.