I keep some scrap for trial-and-error exercises, but I list most of my unneeded construction-grade materials for free on Craigslist. I've had no problem finding people to take huge piles of cutoffs, warped lumber/plywood, etc. The material gets used, and I don't have to do anything other than put it at the end of my driveway.

Plus if you need more scrap for testing, you can get 4' lengths of 2×4 from the cull bin at the BORG for like $0.50 each.

 

Framing lumber, wall cleats. You can often nail/screw that stuff straight enough when it's not for show. Cutting them to shorter boards makes it easier to get rid of the warping - you'll lose some dimension but it's not out of the question to joint/plane them perfectly straight.

 

I harvest the BTUs

 

I keep them clamped together to prevent warping.