I'm trying not to be too vague here, as I suspect a complete answer would require a massive Wiki/DB, but which items are "renewable" vs "scarce" ?
Obviously "boss" parts like Queen Endraga Pheremones or Kayran bits are unique, but:
If I'm looking for silver ore, will there always be some around? Most crafting components can themselves be crafted, but are the raw materials always plentiful, or is there a limited amount of iron ore in each town?
What about monsters, am I going to end up wishing I'd saved more Nekker parts because there are finite Nekkers spawned in the game? Is there a danger of "missing out" on various components, or can I theoretically just grind local creatures to produce whatever I need (assuming sufficient money for the purchasing and crafting labor)?