Plane Sailing
Astral Admin - Mwahahaha!
Typically these will be hidden in plain sight, i.e. they're worn/used by monsters/npcs (even if they don't benefit from them).
Everything else is nice-to-have and can be hidden as well as I damned please![]()
Sadly in the recent modules we've got some of the worst examples of 1e style treasure... magic items which the creatures could use sitting in the chest (dwarven chainmail) or resting on a table (lifedrinker scimitar) and not actually being used by the monsters!