Add coloring pages to your box. Every Sunday my son comes home from Sunday School with a coloring page. He's not much into coloring so he adds them to our pile to add to our boxes. You can also buy a coloring book and carefully cut the book apart and add the pages to your box. Or there are a lot of sites online that you can print coloring pages from. Just google coloring pages or Christian Coloring pages.
This is one of my favorites.