I keep everything in my PSK, Mini FAK, Large FAK, Most of the contents of my Small BOB, Cell Phone and Digital Camera in Aloksak bags. NASDS certified these bags as waterproof to depths exceeding 60 meters (196.85 feet) and under constant pressure of 200 SFW for two weeks without leaks. Though if I ever find myself in water that deep, I probably won't have to worry about the contents of what I happen to have on me being waterproof. <img src="/images/graemlins/grin.gif" alt="" />

Aloksak bags are fairly pricey starting at $4.99 for three 5" x 4" bags and they may be larger than what you want, though you can roll up the unused portion opposite the seal and put a rubber band around it all.

Another option is the Witz Keep-it-Clear or Keep-it-Safe line of waterproof containers. They're about 2.7" x 4.3" x 1.3". I have one of my many PSKs in one of these cases. They're solid. I tested one by standing on it in the bathtub (partial weight), and the seal didn't break, though if I'd put my full body weight on it and squirmed around a bit I bet I could get it to fail. LOL The latch on these bother me because they stick out from the side, and could get caught on something causing the lid to open.

Otterbox makes a few small cases as well. I had yet another PSK in a Otterbox 1000, but my problem with them is that they're so sturdily made with thick walls that you loose a lot of space in the bulk of the material.

Pelican is another company that makes great waterproof cases, but like otterbox, the plastic is thick and it makes their smaller cases seem very bulky.

The latches on both Pelican and Otterbox products are solid and not prone to opening up unless you really intend to do so. However, once again, both are probably larger than what you're looking for. The smallest of these start at about the size of two Altoids tins stacked plus a good inch added to the width with internal space a little larger than one tin. You could probably drive a small car over either of the small cases these companies make and it would hold up. Don't quote me on that last part though... <img src="/images/graemlins/tongue.gif" alt="" />

There're are a lot of other options out there beyond these as well. Check out various Outdoor Sports Stores and Boating Stores and your bound to run across more than a few. I found a bunch last week in REI in the Camping and also the Kayaking sections of the store.