Products and materials that are subject to shedding or particulate generating should be banned from the controlled area e.g. cardboard, wood, and mild steel products that might be subject to corrosion.
There is also the matter of material and chemical compatibility issues with your process, particularly if the cleanroom space and equipment are subject to frequent wipe downs or sterilization processes.
There may well be process specific materials that are also banned. Best practice would be to check all materials with a supervisor when entering a controlled area.