As a thrifty wood worker I am always on the look out for free sources of material for my shop. Lately there are sites that talk about projects that use pallet/skid wood. That wood is usually available for free on construction sites and around factories. There are at least three that I can think of that put the skids out near the road and encourage people to take them away.
There is another source of wood that you might not think about as you are driving around. It is not uncommon for people to put old furniture out for garbage day pickup, or put furniture out with a sign "free". Older furniture often has drawers made from pine or poplar covered by veneer. As a younger and naive wood worker I used to think I was picking up a walnut dresser, only to discover that the walnut was very thin. Newer furniture is sometimes made from birch strips edge glued, not pretty but solid. I've found enough worth while wood that I keep stopping to check, after all if the wood is crap I don't have to take it.
When the knobs are removed and the pieces broken down I have five sheets of thin plywood and an assortment of 1/2 inch and 3/8 inch pieces of wood. I will eventually turn most of this wood into small boxes and bins for tea, toys etc. (box 6 sides, bin 5 sides.)
The tools that I use for salvaging wood are very basic but there are two that I wouldn't be without. One is needle nose pliers, and the other are Linesmen Pliers. The needle nose enable me to dig around and get hold of headless brads and staples and the linesmen pliers have the grip and the grunt to put them out, or cut the off. I try not to use the needle nosed pliers for cutting or prying, and so mine have lasted for years without the tips getting out of alignment.