What cannot be stored in a flammable cabinet?

Excuse me, but could you please elaborate on what items are not suitable for storage in a flammable cabinet? I understand that the main purpose of such a cabinet is to safely house materials that are highly combustible, but I'm curious about the items that are specifically prohibited from being kept inside. Are there any general categories or specific examples of things that should never find themselves within the confines of a flammable cabinet? Your insights would be greatly appreciated.