Even if things do break down such that you need years of food people have the wrong things. You don't need gas for your generator, you need to learn how to live like 500 years ago - without all that. Have enough food to last until next spring, and enough seeds and farming knowledge (which you can get from a few books that you read after the disaster) that you can continue to live off of your garden.
As I said elsewhere, make sure you can share knowledge and work with other survivors. A community of people with various skills (even if you give them the book and they learn it) makes survival a lot easier. Maybe your garden fails, but if you have a few other people you work with you can support each other and everybody lives.