To begin with, you'll need:
A rubber band
A button, paper clip, or other latch
Decorations of your choice
First, build your box. The most simple kind of box is a square. Simply cut six identical pieces of cardboard and make a cube, taping the corners on both the inside and outside. For the top of the box, only attach it on one side so it can be the lid.
Optional: Separate your box into sections by cutting thinner strips of cardboard and forming a grid. Once you tape down your horizontal strips, you may just make cute going not quite but almost all the way through, and inserting the vertical strips in them.
Next, make your latch. Attach a rubber band to the lid opposite where it is attached. On the side if the box below the rubber band, attach your latch or hook. To close the latch, put your rubber band around it so it catches and doesn't open.
Now is your time to be really creative, and decorate your box however you like!
This is Molly's box, decorated with stickers and dot paint.