Sealline Seal Pak
There's nothing handier on the water than a waterproof hip pack. The only problem is all your buddies will be giving you their essentials to store. You can strap it around your waist or remove the waist strap to use it as a shoulder bag. It's got a roll top closure and a pocket on the outside.
Weight: 207g (7.3oz)
Dimensions: 20 x 20 x 8cm (8 x 8 x 3")