If you're ever stumped, roll on the random trinket table for intelligent monster "bits". If the Players haven't memorized the table, and you act like it's a real valid magic item, your players will love the gear. And there are a bunch of "what's in my pocket?" tables on the internet kicking around.
As for monster bits, make sure you enforce time on this. If you have random encounters in your game, and there's a 20% chance every ten minutes, and the PCs take 10 minutes each fight to strip a monster of any interesting "parts", they're making an interesting game decision! And that's always a plus.
You can always go with the magical component route, but I'd also tie it to bragging rights. Have items that can be made into clothing. Or mounted on a wall of the PCs' house. Doing stuff like this means that the PCs aren't just trying to get more treasure ("greyhawking the dungeon"), but actually get something less tangible out of it. In my experience, that's what this behaviour is aiming for - not a mechanical gain, but something more ephemeral that feels more "creative" and reflects a character's past exploits more than mere experience points.