The Post Carbon Institute and its companion site Global Public Media have focused on relocalization as the best response to Peak Oil, and provide quite a bit of information on the subject. PCI is also coming out with a book on the subject in the fall. WELL in Willits CA is a good example of what a community organization for economic localization can be.
But in most places the communities as a whole (or just too large a segment thereof) simply aren't ready for this process, the agreement and participatory democracy that it requires. So what can one do under those circumstances?
I started thinking about this in response to a brief comment from lahermite. Suppose you live in a large city or suburb, where people aren't very forward thinking or open to such ideas. Well, start where you are. You've got yourself, your household, your friends, their friends, and probably a bunch of other people you haven't met yet, some of whom you could reach through certain organizations or publications in your area. Even if it's just you, that's a place to start. It won't seem like much on the grand scale, but your own life (and your energy bills) can only benefit from whatever you accomplish.
Ask yourself: How can I make my energy and food more local and sustainable? Get everyone together and start a brainstorming session.
Can you lower your energy needs ? Can you find cheap ways to harvest solar energy, like solar ovens, or recycled solar panels? Can you buy local organic food? Can you grow local organic sustainable food in your own backyard, with an eye towards actually supplying the basics of your own diet? Can you start a community garden that includes a study site which models what one person would need to do to grow all their own food? Can you team up with sympathetic organizations that can assist your small group in doing these sorts of things?
The possibilities are really endless, and many would be inspired by the particularities of your area. Target whichever projects are most important to you and most practical with your given resources and needs. It is likely that as the price of gas goes up and the need for local economies increases, awareness will increase, and your group will attract more and more people. Bear in mind also that the simple existence of your group (and whatever accomplishments people hear about) will indirectly increase awareness of these issues in your community.