How about collectibles, special and super rare items in pieces of 7?
Similiar to SwG thing really, you gather these and when you have all the parts you take it to the specific craft to finish it.

Or Bullets of varius sizes, they'd work just like USD (so for nothing other than another possible currency or if you decide to add gunpower etc in the future)

Im not sure, i just want even more junk amongst the junk...

Remove the "you cant find anything useful" and make the scavange succeed 100% but let the player decide what is junk and what isnt.