I find it the most difficult thing in the world to walk passed a rubbish skip that is loaded with clean untreated wood, builders timber off cuts, bricks or just about anything else that can be given a second life. The wood burner at home runs off free timber from a variety of sources including, some coppiced, some found in alleyways, or picked up from a local furniture makers, or scavenged from rubbish skips. Supermarket skips are also another good stop to pick up wasted resources for free, and as I am sure you will already know, Supermarkets throw away perfectly good food on a daily basis, UK Supermarkets throw away around 2 million tons of food a year, some of which has never even reached the shelves. One recent find that whilst out and about in Bolton was a pile of thick broken down cardboard boxes, we simply picked them up out of a warehouse trolley, stuck them in the van and they are now in the raised beds covered in horse manure, which was also free.
There is loads of useful stuff out there waiting for you to pick it up, go forth and scavenge!
Wikipedia Article on Freeganism
Steve