One of the first things (maybe the first thing?) I printed on my Prusa Mini was the whistle model that came with the printer. It's a quick, useful print, but it has one problem: It's easy to drag out of your pocket without noticing.
After printing a few more to replace lost ones, I decided enough is enough.
(click for full size)
Mine is heavily inspired by Prusa's model, but comes with a holder you can put a string through. Hang it around your neck, or attach it to some piece of clothing. It works pretty well (and is very loud). I'm sure it can be improved more to get a better tone out of it.
Check out my OpenSCAD model, if you want to print your own.