I wanted a neat, sturdy holder for sticky notes; and whilst looking online for ideas on model, I stumbled upon the concept of having a stencil integrated. I implemented this as having slots on the sides of the holder, allowing a lid to be easily placed; they are designed as such that the lid has to be in a vertical position for it to be removable
The pre-generated models are designed for this particular type of sticky notes: https://www.clasohlson.com/fi/Muistilappukuutio-viivoitetut-arkit-101-x-101-mm/p/44-2292 - however, adapting these should prove relatively easy with the included OpenSCAD file. Note that you require Belfry OpenSCAD Library for generation to succeed.
A sturdy material and reinforcing printing settings are recommended, considering this is a functional print expected to be handled somewhat roughly. Example was printed with Prusament PETG; 4 perimeters, variable layer height (max 0.3) and 30% infill for the base. The lid was a more experimental one, with no top or bottom solid layers, 80% infill in picture (lesser should work, e.g. 60%), and minimum of 3 perimeters.
The author hasn't provided the model origin yet.