West Marine used to have a jet-ski pack ($29) that had a smoke flare, a handheld flare, a dye marker, a reflector and a spot for an inflatable marker that was roughly the size of a couple of blackberries stacked up.

Don't know if they still sell them, but I bought two for long distance stuff (never had to use them)

I have used the "sausage" when diving offshore a lot. Good idea for sailing. You do have to inflate them manually, though, which may not work for an unconscious swimmer, but it's better than nothing..