I'm fortunate enough to have a great five mile river section that has some class I-II river that is 20 minutes from my office, and when weather allows, myself and a few others from the office (who as well have packrafts) can blow out around five o'clock and make the approx. two hour trip. Said river is dam controlled so it stays runnable about 350 days a year, which allows for a lot of trips, however I was never really happy with a 10L dry bag strapped to boat, as it tends to bounce around.
I like alpacka's solution for a front pocket, however it for one it is outside my price range, and two it lacks the top daisy's that that I like to add some shock cord for strapping any additional items to it since I'm covering the front tie straps. A simple 8" long water resistant #5 zip coil on 200psi water repellent VX21 is large enough to to get anything in and out without fuss, but not too big to make a huge gap when unzipped in sitting duck position, hence the location of zipper in top of pocket.
Total volume is 15L and total weight is 4.2 oz. We will see if it stays as is but right now it seems like a nice solution.
As a side (well stern) bonus, a simple strap and strap sleeve on a soft sided cooler, after finding the correct angle, I've found a way to keep the cooler upright and was lucky to find a cooler with the zipper operable from the sitting position.
By keeping the cooler on stern, any condensation or ice melt, no extra water is introduced into boat. Any questions feel free to fire.