Permaculture is a system wherein you grow as much of your own food as you can, and live off the land you have available to you, by planting plants to grow food (among other things). When you do so, you save yourself quite a bit of money by not having to buy as much food. You reap health rewards because the food you grow yourself is fresher and not covered with unknown chemicals. You help the planet by reducing shipping of foods to your local store, and you add biodiversity to your landscape (especially when so many people have nothing but grass lawns).
The plants I am listing are ones who produce massive amounts of food for the space and time they consume.
Fruit Trees
Depending where you live - you may or may not be able to grow many varieties of fruit trees, but if you can they are simply wonderful. Not only do they supply you with fruit, but they are beautiful in the spring, and help other living things, which may in turn help us. Honey bees, for example, you help them, they help us. A fruit tree will provide you a bounty every year, as well providing some shade for other plants or the yard.
Some fruit trees require a pollinator plant, so make sure you know what you are buying, I prefer to have several different types of fruit trees, as space allows. Apples are probably one of the most hardy for northern areas. Plums, pears, and cherries, are other fruit ideas. I would suggest at least having three different trees so you have different maturity dates, and a nice variety of fruit. When the trees are older you can share your harvest with family and neighbours.
Fruit trees generally require a lot of water to get bigger fruit, and by thinning some of the smaller, or deformed, fruit in the late spring you can increase the size of the remaining fruit.
Potatoes
It is possible to live a long time on potatoes alone, not a thrilling diet perhaps, but it is good to know if you ever run out of other food sources in an emergency situation. Not all potato types produce as well as each other, I have found some of the more colorful spuds do not produce as many potatoes as the yellow or white varieties do. Still I like having at least three varieties, early maturing, medium, and late.
You have to buy Seed Potatoes from a store, and cannot just plant the ones you purchase for food. These have been treated so they do not grow, and while you might get some production from them, it will be limited compared to what you get when you start with an actual seed potato.
Because they are underground you can plant them a bit earlier than most crops. Once the ground is soft it should be worked and the potatoes may be planted. When they start growing, you need to "hill them up", covering the bottom of the plants so you get better production. Exposure to the sun results in them becoming slightly poisonous, you can tell if they have been exposed to the sun as they turn green.
Young potatoes are ready to be dug up when the flowers have faded and begun to turn to seeds (not the same as seed potatoes). You harvest these new potatoes by lightly removing the soil and keeping the plant intact to grow more for a later final harvest where the plant is dug up.
Tomatoes
Tomatoes have health benefits and are fairly easy to grow. The biggest problems are cold temperatures killing the plants or too much water causing rot problems. Surprisingly there are many different kinds of tomatoes and they actually do have somewhat different tastes. There are even yellow and orange tomatoes, large ones and small. I suggest growing two plants per family member and freezing excess tomatoes to use in sauces.
Zucchini
These guys are on the list because they are so easy to produce and will continue to produce until frost kills the plant. Zucchini are tastiest when they are smaller, but may be eaten even when large. If your zucchini get too big you can use them in baking or feed them to any livestock you have, including chickens or sheep.
They may produce so well you will be forced to leave anonymous zucchini on your neighbours porch.
Lettuce
I generally buy a bag of mixed lettuce seeds and plant them on a border of the garden, and never have a shortage of lettuce throughout the summer. We actually have pet walking stick insects whom we feed some of our lettuce too, but still have a surplus. Lettuce is not really a good survival food, but is one that many people enjoy throughout the summer, either the main staple of a salad or a small filler in a sandwich.
Lettuce may be bothered by slugs which can be controlled by spreading sand next to your lettuce row.
Strawberries
A ground cover that will spread over a few years and offer you some early eating. Strawberries produce well when the weather is cooler and they receive a good amount of water. When they spread the new plants can be moved to other parts of the yard or garden. There are many varieties of strawberries, early, late, and everbearing. I prefer everbearing types as I enjoy having an ongoing crop throughout the summer. You should consider an alpine variety in places where you do not want spreading. You may wish to preserve strawberries as jellies or jams, or they can be frozen. Try adding diced strawberries to a salad.
If your garden is in a hot area, you will need to plant your strawberries in a shadier location.
