The most important thing a concerned consumer can do is buy local produce. If you don't, ask your produce grocer where your food is grown, and encourage them to purchase from local growers. For your own health, and the health of the land, you should also encourage them to buy organic. It is also important to recognize where good agricultural land is located, and preserve it. Once good ag land is paved over, it loses its biological components and even if the asphalt or concrete is removed, it would be decades before it could become fertile again.
Urban sprawl destroys ag land.
Only a few wealthy companies benefit when we ship the power to feed ourselves overseas. We all lose in the long run. If retaining our nation's food base is important to you, write your state and federal legislators to let them know of your concerns. For further information, see the website for American Farmlands Trust.