Hitchwiki has a lot of useful general and location-specific advice on hitchhiking, including an interactive map of places where people have tried hitching and reports of the results. In many parts of the world this is a great way to travel for free while seeing more and interacting with more people than one otherwise would when travelling. I've found it can be as fast as travelling by bus, and get you places buses don't go. (Even crossing an ocean isn't a dealbreaker if you're willing to hang around marinas for a few weeks offering to help sail/cook/etc, though I haven't tried this.) The associated
Trashwiki might be useful for the "food and beverage" side of things, though it is much less extensive as yet (Hitchwiki itself occasionally has info on missionary food and the like).
Couchsurfing of course has been discussed in this forum many times (though if you're hitchhiking you should also be prepared to camp in the middle of nowhere if necessary).
For a completely different approach to travelling free,
Free Frequent Flyer Miles and
Frugal Travel Guy (as well as the miles&points forums here at Flyertalk) provide advice on racking up thousands of frequent flyer miles and hotel points entirely through credit card offers and similar promotions. Sometimes just opening a checking account or making a single purchase with a new credit card yields enough miles for a free roundtrip flight.
Of course, neither of these approaches works perfectly reliably in all situations. I find it most effective and rewarding to combine the two, e.g. arriving in a city hitchhiking in the back of a pickup and departing on a business class award ticket (though I've never found hotel rooms to be worth the points or money compared to hostels/camping/couchsurfing). Even then, it's pretty difficult to NEVER spend money, but I've definitely travelled for much less than I would have spent if I had stayed home.