I've mentioned before that I use Japanese hand saws and that they are well worth having a couple in your tool bag... That said, most of the Japanese hand saws are less than happy in western tool boxes and I keep meaning to sew up a suitable scabbard to protect both my saws and my toolbox-questing-fingers (FYI, Japanese saws are wicked sharp).
Not much bigger than a pocket knife, it is just the thing for the sort of trim work most of us on boats tend to pick up the hand saw for and also looks like just the thing for dovetails and other wood butchery.
Better yet it's cheap at less than $10!