Use Ikea Knuff magazine files as under sink storage holders. Screw a magazine file holder to the inside of kitchen cupboards. Add space to store more bulky items like chopping boards, cleaning products etc.
Like shipping pallets, wooden cable spools are another item that is usually found for free on Craigslist. Since cable spools are limited by their shape there are fewer repurposing options, but they make a great coffee table bookcase.