I use christmas gift bags, they don't all lie flat, but for the most part they do. I have a book shelf full of bags and that's how I stop myself from starting new projects, no bag, no project!

Unused pizza box.....

that's a great project.

I use a clean (never used) Pizza box. It allows you to lay your blocks flat in it and when the lid is up...I use that for a mini design wall. When the top is closed it is my mini desk top to work on. Since it is just a Pizza box, I add a loop of elastic through the cardboard and a button(big hole to put elastic through) for a closure. I just push the elastic through holes that I made and tied a big knot on the ends to keep them from pulling through. You can add other loops of elstic for whatever tools you want to fasten in.

Ditto the new Pizza box

LOVE this - how pretty and practical at the same time! Thank you so much - this is perfect! :)

I use the pizza box as well. But I do add elastic to the botton [through the hole that are already in the box] to keep the blocks flat.