Micro Stash Tube
A simple no nonsense screw top tube with an 'O' ring seal. Approx 40mm long they can be hidden almost anywhere and if the need arose you 'could' swallow it to retreive it later. Alternatively, could easily also be 'stashed' internally easily, in other locations.
Clear walls allow you to view contents.
A perfect addition for storing water sterilisation tablets in a survival kit for example, possibly one of the few things that has a hundred uses and the more you use it, the more you will find.