Answer:
Obtain any material that can be carved, something to carve it with, and a ruler. Carve from the material a cube whose edge length is a foot. You now have a cubic foot of the material. Fashion a knife of this material and use it to cut a cake; you have now divided by the material (get it?), leaving you with just a cubic foot.
Alternatively, make sure the area of the bottom of your foot is one square foot. If it is, then you have a square foot of foot. A square foot times a foot is a cubic foot, so you have a cubic foot.