I use a Survival check (based on the CR of the critter) to extract the part from the critter... And then a Craft (Alchemy) check (generally at the same DC as the first one) to refine it into whatever form you need it in to function as a component for a metamagic component, magic item bit, or whatever... In general, anything can be useful as a component for something, so long as they are thematically linked.
Parts to be so used 'go bad" pretty quickly, so as to keep the players from dissecting each and every critter they come across.
Later
silver