When I was a kid, we used to bike to these newly housing development and we would take their used woods from their dumpster and we would build stuff with it. So proud when I was able to build a dog house for my dog and build a treehouse to play in.
Dumpster diving was still legal but I would not do that again. Even if you dive into their dumpster, it is still grounded for trespassing and is frown upon.