Our homeschool room bookshelf had become untidy and very disorganized so I came up with a solution that works great and lets you reuse old cereal boxes for a greater good.
They are very simple to make. First, gather some empty cereal boxes of various sizes (note that only very similar sized ones will work with stacking though!). Cut out either the front or back leaving a very small rim around the side and do not cut any of the edges of the box (you'll need to poke a hole in the cover with the scissors to cut the cover off.)
The only other thing you need to do is staple the top opening flap part of the cereal box (which is now a side). You can glue or tape it also, but stapling works the best.
You can also glue/staple on a piece of construction paper to the front side and label it with whatever it is the box will be holding. I knew saving all of those cereal boxes would come in handy some day!