Sounds like a wonderful project. Don't have any advice to offer from experience, but look forward to seeing the project develop.
Few thoughts...I may have missed the solution, but could you have the flag section placed from the back to place/secure the flag and his other items, and then make a hinged door for the section with the coins that need to be accessed? I see the bottom section goes below the flag part, so perhaps the hinge on the right and some type of magnet to hold it closed?