What I use, though not water proof, is a plastic container orginally used to hold a US Military Personal Decontamination Training Kit. It's size is about like stacking two packs of cigaretts on top of each other.
I have one in each car kit that I have. They are stashed in a grab and run bag if I am unabe to take the full kit with me.
In the plastic container I have a small mirror, snare wire, braided fishing line, hooks, sinkers, golf pencil, tampon, matches, razor blade, small knife, magneisum/flint bar and a few other small items.
The lid of the container is teathered to the main body of the container and there is s small hook that can be attach the continer to something.
One other suggestion for a small metal tin is to use a couple of the round "Altoid" sour's candy tins.
Me personally, I like my black or OD green plastic boxes.
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