Checkout the feet on my rotisserie:
To make it stable, screw down the "foot" (large bolt) untill it makes contact with the floor and a turn or so more. Yes, as Pop said, it will move about when working on it. I can move my shell easily but need it to be stable when working on it. You might be able to design an arrangement like this for a workbench.
chris
As for your other "problem". I'm not sure what to think of anyone who does not have cupholders on his toolbox, workbench, etc, etc. j/k