Underwater notepads are simple, cheap and you can make sketches...

https://www.divegearexpress.com/unde...lue-cover-2600

Archaeologists and marine researchers use them. Too bad we gave up cuneiform. The Sumerians, along with the Greeks and Romans, used wax tablets for non-permanent note taking.

I've often considered one of those digital voice recorders, e.g....

https://www.amazon.com/Recorder-Lect...voice+recorder

for those middle-of-the-night inspirations. I wonder if it could be waterproofed. If has voice actuation so I suppose it could remain outside the shower. With the actuation level turned down, it might ignore shower noise but pick up loud speech.