I used to do alot of diving off the coast of Fla. so I would keep vital personal documentation and a First-aid kit in a Pelican Water tight box.
Pelican Cases I have had mine to depths of about 150 feet without any problem. They make them small enough you could make a nice little belt size fire kit
Hope this helps, remember depending on the depth you go you have to worry about the pressure applied to the outside of the container.
goat