I left a comment here: https://lemmy.world/comment/25979420
In general, I would glue 5 pieces of cardboard using paper to make the underside of the box. Then I’d put the items in and glue on more layers to fill in the leftover space. After finishing the top layer, I’d leave the items inside the box for a few days to dry and shrink
After that, you can add more paper to make the surface harder, or glue on anything you want.






I tried acrylic paint, but it prevents me from making adjustments afterward by gluing more stuff on. Maybe I’ll try watercolor or felt