Little box in the shape of a question mark.

thingiverse

I've rewritten the instructions for my brother-in-law's birthday gift box. So here are the step-by-step directions on how to present his birthday cash: Print out this box template. Carefully insert the birthday money into it when you're finished. The fit is really tight, so avoid forcing it shut if possible. To make a more dramatic reveal, try adding some glue or acetone with the closure to give him a real sense of excitement.