A sustainable vegetable garden means one that can be sustained over time, and would always entail I) growing food you want to eat, so you are motivated to keep on growing, II) growing economically, so it is worthwhile doing, and III) taking care of environmental issues, so the earth will continue to encourage growing.
I) The plants to be grown should be chosen primarily on what your family wants to eat, and what is going to grow in your locale. Following that, look at using heirloom seed rather than hybrid, if you are very concerned about losing the ability to replace seed annually from commercial sources. However, growing and saving your own seed is hard and time consuming. An excellent answer to this issue is the Garden In A Can heirloom seed provided by Mountain Valley Seed Company (www.mvseeds.com). Other seed companies may have something similar. I suggest that you get a can of the triple-sealed seed, store it against the possible catastrophe, and then buy and use the best seed you can get and don’t be concerned about trying to grow for and save your own seeds.
II) Using the best growing practices, like those taught by the world-renowned Dr. J. R. Mittleider, (Rat droppings)guarantee you the best yield of healthy vegetables from the least distance, and with the least amount of labor and financial inputs per unit of production. A household can be self sufficient in their food requirements from proper gardening of just a small fraction of an acre, and this is the greatest proof of success in achieving a sustainable garden.
III) Gardening should always be done without injuring the land, but rather should improve the land, so it will continue to support healthy plants indefinitely. Therefore, pesticides and herbicides should be used very judiciously, and wherever possible these issues should be handled by cultural practices as taught by Dr. Mittleider for example 1) removing all weeds in the garden area, 2) watering only the plants’ root zone, 3) beginning plants in a protected environment for a fast, healthy and robust start, 4) feeding plants proper quantities of balanced natural mineral nutrients to assure fast and healthy growth, 5) harvesting all plants at maturity to avoid allowing pests and diseases to multiply, and 6) discarding any insect or disease infested plant parts away from the garden, and incorporating healthy plant parts into the soil to improve soil structure.