I'm a big fan of perrenials - things that you plant once, and then only require minimal work to maintain and harvest. Things like fruit trees and berries provide delicious fruit that can be storred in the form of preserves, cider, etc.

I also reccomend Hops, which are extremely hardy once established. While they don't provide calories, they are a valuable trade comodity for homebrewers, as their is currently a worldwide Hop shortage. They also have medicinal uses, and of course you can use them to brew your own beer.

While not exactly gardening, I highly reccomend cultivating mushrooms, since that offers a lot of return on your effort, and can be cultivated in heavily shaded places where you would have a hard time growing anything else. Mushrooms also make a valuable trade commodity, and can be dried for storage. If you have access to freshly cut logs, they can be innoculated with mushroom spawn easily and fairly cheaply, and will fruit(produce mushrooms) for years afterwards- about 1 year for every inch of the diameter of the log. 2 good sources for mushroom spawn and information are Field & Forest Products(www.fieldforest.net) and Fungi Perfecti (www.fungi.com). Note that the print catalogs from both companies have a greater selection than the website.

One last plant I would reccomend is peppermint. Once planted it grows like a weed and will spread in no time, yielding lots of delicious and medicinal tea, which can easily be collected and dried as well as used fresh.

edit: I second the garlic reccomendation. It is very easy to grow, and can be planted in the late fall as well as mid-summer, yielding two crops a year in the same bed. I've got 2 beds of garlic growing right now in the middle of winter, which will provide all the garlic we can use in a year plus some to trade.