This one is fairly simple and very straightforward.
So, you have a bag of marbles and can no longer find anyone that "plays" marbles? Have I got a plan for you !
Step 1: Ingrediants...
One cardboard box, able to hold about 50+ marbles, and also thin enough to fit inside a medicine cabinet.
One bag of marbles, about 50 or more should be enough.
The cardboard box should be completely enclosed with a small flap on the broadest side (front or back) for the opening.
Fill the box with the marbles, close the flap, and place it up-side-down inside the medicine cabinet, carefully closing the door to hold the flap closed (if your chosen box has no flap that extends to the broad side, you can cut one, as illustrated, so you don't have to turn THIS box, bottoms up. . .