It turns out I have been using my kid's toys to help me think about voxels and other algorithms. This is by far my favorite:
This thing really helps. Some of the work you do with voxels becomes a lot easier if you have a way to look around them with your eyes instead of just your mind.
Several of these cubes now have little annotations done by me with a sharpie: numbers, face indices and other stuff like that. These numbers can also be found in the source code.
Here is another time saver:
No need to waste paper if you just want a temporary drawing for something you need to understand.