Hello sweet angel
Mine is the same as the one in the link from TheWog. It's measurements are:
Keep-It Safe®
Size: 2.7" wide x 4.3" high x 1.3" deep
Features: Solid Color / Nylon lanyard with breakaway clip (or carabiner) / Portable size / 250% larger than Surf Safe® / 6 colors
Function: Waterproof container for several small items.
My plans are for it to store my KTTW keys, driver licenses, copies of our passports, some cash and a sunblock stick. I put it in there to try it out and it all fits.
It floats, so you can wear it on top of the water snorkeling or stow it in a gear bag somewhere. I don't know really how waterproof it would stay if you took it underwater, since it only has a small rubber seal and a pressure-latch kind of system.
Good luck!