advice/solutions for an "optional" 3rd leaf?

So my room-within-a-room practice room is actually one of 2 rooms within my garage. The other room is framed on 2 sides by the main outer wall and the new, freshly-built room. I'd like to be able to hang things (various tools, etc.) on the outside of the freshly-built room walls. Seems like the easiest way to accomplish this would be to put some sort of cover on these walls. I'm well aware that the common convention is to leave these types of walls unfinished since covering them would result in a 3rd leaf. However, is there a more preferable cover (other than drywall) that might be less 'third leaf-y'? Perhaps that type of soft particle board with a evenly spaced grid of small holes? The type that you see hammers, etc hanging from in some old-school garages? Or am I sweating this too much?