Buy a large metal safe. Concrete it into the cellar of your house. Put the picks in a box and place it in the safe.
From then on you will know EXACTLY where your picks are....

Actually -if you are concerned about problems from sticking a container onto your instrument, why not attach it to your instrument's strap. At least if you then lose your flatpick, you will also be strapless.
Quack!
GtD.