I like the pizza box Idea that would be great for stacks of finished squares. They would stay flat and not wrinkle. I also like shoe boxes and the other storage item I collect are those heavy plastic bags you get with things like curtains/ shower curtains/blankets/some bath and cosmetic products. Because they are mostly clear plastic and some even have Zippers. and are lots of sizes. Gift boxes like for shirts go on sale after the holidays for cheap and come in diff sizes!