I LIKE the waterproof bottle idea! This is the best suggestion I have heard yet!
I have always thought it would be cool to hang something useful from the hook,(like a six-pack of beer), but anything useful seems also to be too heavy to be safe. (Imagine during a jybe getting a six-pach in the head!)
A small waterproof bottle shouldn't hurt much, unless you get hit in the eye.
Then, I've always had the fantasy that an adventurous lovely lookin' crew might want to hang her bikini top fron it, while getting that little extra sun. -But alas, my crew seems to always look more like Garrison Keillor or Woody Allen.