I always keep about 200 of each type in the stockpile in case I need it.
(Need sutures, need clothes, need to satisfy a retard's mandate, need to satisfy a mood...)
I also hold on to thread for the same reason.
I also buy *every* kind of gem, and raw glass, and at least 20 bars of each kind of metal.
Sometimes moods demand very specific materials, instead of generic ones. Eg, "I must have precious fire opal!" Or "I must have pigtail cloth!"
This is lost in translation with posessions and secretive moods, where the specific gem, fabric, metal type is not specified. It is only stated in the fey mood type. The other moot types will just say enigmatic "metal bars", "sparkling gems", etc.
I don't know if such specificity is present post 40d, when I first experienced strange moods, as the default methods I developed for dealing with them have not warranted deep investigation. I just know it was true then, and could be true now unless toady changed it. He might have, because moody dwarves used to demand impossible materials, the most infamous being crystal glass, which could not be imported in the 40d days, and could only be created with raw rock crystal gems, which were more rare than sapphire from my experiences.
(Something I took objection to, since crystal quartz is laughably common irl, to the point of being worth 50cents retail at gift store kiosks for fairly large hunks of it.)