Enter: the "Freebag"....
http://www.sailorsams.com/mall/freebag.asp
Fundamentally it's a small beanbag chair, but we've found no end to the utility of the two we keep on board. In addition to general cushion use (we have no actual cockpit cushions), swimming-toy use, actual luggage use, etc. I often use a freebag for sitting on the coaming for better visibility if I have the dinghy on the foredeck, or if we're in a patch of water that's lousy with lobsterpots.
There is a bit of a learned art/skill to getting a really comfy setup, but once you've got it you're set for hours. Usually I just sling about 2/3 of the beans over the edge of the coaming (so that they bear your weight on the side deck) and jam the remainder up against the winch. Plop your butt down, wiggle here, scootch there, and voila!
Apart from the above website that Google turned up when writing this post, I don't know where to buy them. We haven't seen any since we purchased our pair at BoatUS two years ago. If you find a good source, let us know, we're constantly fighting over them, and could make good use of a third. ("or fourth", Julia would be quick to add)
