The skateboard would literally be a plank on top of some wheel axes pinched from a shopping cart, the scooter would just be a flimsy pole stuck through a hole in the "skateboard", the bicycle would be 2 such poles, one with a small piece of wood as a seat and at the front the wheel axis had been moved to be soldered to the front pole so that one rotates with the other.

All of them function only in the technical sense, are awkward to use, don't last long under continuous use and look like shit because they were not done with the right techniques for resilience and have none of the finishing touches needed for ease of use and attractiveness.