I usually have a notebook in my shirt pocket, and to use it you need a pen or a pencil.
You can either have a pen (or several) with a "pocket protector" and become the un-cool type of nerd, or 3D print a pen/pencil holder for your notebook that caps and protects the tip of your favourite tool (and shirt for that matter).
This holder is designed to work with the short pencils you can get from IKEA (and other places), but it should work for any "shorter" tool with a diameter of around 7 mm (1/4 inch or a little more).
The first I printed with 0.24 mm layer thickness and the second with 0.1 mm. Both work fine, but the 0.1 one looks nicer (dough!).
PenHolder.stl |