The Shoreline Marine drink holder, the RoboCup patented portable caddy clampable drink cup holder and rod holder, the SkiffDaddy drink/beverage/cup holder and caddy, and the BoatMates Cruisin caddy are boat cup holders. Each of these boat cup holders has at least a 4.4-star rating on Amazon.com as of January 2016.
The Shoreline Marine drink holder folds up and has a 4.4-star rating. It fits in small areas, adjusts to fit any bottle or can and has stainless steel hardware.
The RoboCup patented portable caddy clampable drink cup holder and rod holder clamps to flat and round surfaces and holds two drinks, cups or bottles. It also holds rods, poles, flashlights, tools and phones and can be used for fishing, camping, hunting, golfing and office use. It has a 4.8-star rating.
The SkiffDaddy drink/beverage/cup holder and caddy is made of hard-drawn steel and coated with PVC, and it holds bottles, glasses and cups. It can also be used in kayaks, canoes and lawn chairs. It fits on 1 1/4-inch-square horizontal tubing and has a 4.6-star rating.
The BoatMates Cruisin caddy has a 4.5-star rating and mounts with screws or cushion cups. It is constructed of resin and is simple to organize.