Consider canning and fermenting some of your food. Also, grow things that can last throughout winter, such as potatoes, carrots, beets, etc. They can last in a cool dark place for months. Broccoli and Okra can be blanched and flash-frozen. Cucumbers can make pickles.

There are tons of good ideas out there about preserving your own food. But, I agree, that a small garden won't take a big bite out of your food needs. You're not trying to become self-sufficient, you're trying to lower your reliance on store-bought food.