DIY hanging holders
I made my own out of some heavy-gauge wire, coiled at the bottom and spiraled 2/3 up the side of a bottle, then hung from my stern rail. They aren't good for coffee unless you put it in a bottle first, but they are in easy reach for booze cruises. For coffee, we just tacked a little of the under-rug non-skid stuff to the bottom of some of our mugs, and they stay put pretty well wherever you put them.