I have gained a great respect for people who build tiny houses out of reclaimed materials! I decided to use the boxes that my last two windows came in for the shelves in my rolling pantry... Just getting the boxes apart and all of the giant staples out took a few hours. Then I spent two hours sanding all the residual tape/labels off and filling in the staple holes etc...and that was only one box. I've got another one to go. Each box yields four shelves, meaning that I don't have to buy two 1x6's. Saves me about $12. But I also live by the motto "No money, but plenty of time."
Here are two of the shelves, after scraping but before sanding/filling.
Here are a couple of shelves that actually are being shelves. All filled and sanded. Yet to be painted.