A stat block rarely refers to equipment, other than armor or weapons used by a monster. A creature that customarily wears clothes, such as a humanoid, is assumed to be dressed appropriately.
You can equip monsters with additional gear and trinkets however you like, and you decide how much of a monster’s equipment is recoverable after the creature is slain and whether any of that equipment is still usable. A battered suit of armor made for a monster is rarely usable by someone else, for instance.
If a spellcasting monster needs material components to cast its spells, assume that it has the material components it needs to cast the spells in its stat block.