Grow your own food. If you live in a house with a backyard, devote a part of it to a vegetable and fruit garden. Find out which foods are native and easy to grow in your climate and area to minimize the gardening that must be done in order to grow them. Even if you live in a densely-packed urban environment without access to a yard, many foods are easily grown in indoor pots and window boxes. Greens like spinach and kale do well without a lot of sunlight, while fruits like strawberries need only a very small space to take off. Some health foods like wheat-grass grow very quickly in very small spaces and offer densely packed nutrition profiles to those that consume them.
Practice foraging -- the act of obtaining food and other necessary items from the environment around you, both urban and rural. For most of their existence, humans were hunters and gatherers, foraging for most of their daily provisions. If you have access to wilderness areas, like state or national parks, learn about the edible foods that grow in your area, while providing yourself with nutritious meals. In northern climates berries and nuts are usually easy to find, while in tropical areas palm fruits like coconut and banana abound. Even deserts contain a variety of edible cactus species.
Learn to fish and hunt. Fishing and hunting are the fastest ways of providing solid protein and serious calories to your diet directly from the land. If you live near public spaces that contain rivers, lakes and lagoons, chances are that legal fishing opportunities abound. Hunting seasons and restrictions vary with locale and season, but those who become proficient at this skill often pack their pantry for the whole year in just one season.
Learn about medicinal herbs. Although modern medicine is necessary for dealing with serious health concerns, many minor ailments and first aid issues are easily remedied by natural herbs. Grow a small herbal garden if you have the space or simply forage for native herbs, being careful not to pick any species that may be endangered or protected in your area.