So I started wondering if there are any “pro machinist” shortcuts for making cubes.
It’s all about the CNC machine one uses, the fixtures one has immediately available, and the machine tools available.
Doing a cube on a 5 axis machine is is very different than a 3 axis machine. Is one limited to a vise or does one has a sea-of-holes and some fixturing gadgets?
Machining curved surfaces (and spheres) are much easier with a 5 axis machine than a 3 axis machine as you might imagine.
"We shape our tools and thereafter our tools shape us” - attributed to Marshall McLuhan
Rather than try to explain many of the methods, let us know what gadgets you want to limit the exercise to. Then we have lot of fun! 
For instance, with the flip jig: mill the top half of a cube - 5 and half sides - flip and do it again. This limits the quality of four sides. Clean them up if a fine finish is expected.
mark