Oh god I fear I've gone full middle-aged suburban white dad. For a minute there I was seriously considering trying to 3D print some kind of utility belt for holding a coffee cup.
But like...it's cold, so I want to bring some hot tea for the walk. But it's cold, so I would like to put my hands in my pockets not have to be holding the cup! I mean I could modify a bag to keep the cup upright easily enough but it'd still be a two hand operation to get it out and put it back...with a belt clip it could pop right off with one hand!
Sometimes I can just pocket that shit...but only if those aren't already filled with books and electronics...