I bought a load of these from an Ebay supplier;
...ideal for small caches. They have a silicon seal, strong clip, are made of good solid plastic with robust hinges and are designed for military use, as waterproof containers for keeping small items dry in the field (tinder, survival gear and so on). Luckily, I bought enough for a whole series of caches; they're just the right size and shape as they have enough room for several geocoins, a good-size log book, a pencil and a few small swaps. Also, being fairly flat and the right shade of green they fit in to a remarkable number of places. Great! Miles better than the usual tupperware-type thing. (N.B. the watch is not a swap item!).
But I can't see anywhere that sells them any more: anyone else use them?
I should mention that they sell for £2.99 each: not bad!