I recently made this 'discovery box' for Miko and he is at a great age for exploring this type of thing. For now I have filled the box with different scraps of fabric but you can put anything inside really. In fact, Miko likes to figure out which other toys and objects can fit inside.
I saved a lid from a disposable bag of wipes and glued it onto a cardboard box (a box of oatmeal in this case). Then I covered the box with scrapbook paper, and finished with a layer of clear tape. Miko still likes to gnaw on things so the tape keeps the box and paper from being edible.
This activity was so quick to finish and has provided countless minutes of fun for Miko already. I'm thinking I will make another larger one soon too.