re: What to use to make a rattle rattle?

If I was going to use anything metal, I would probably use stainless steel (like these do).  You could also find some beads.  Heck, go to Jackalope and buy cheap bag of of beads used for making jewelry.  

I think that maracas sometimes use wood beads.  Of course they are usually much larger.  Wood pieces do not necessarily need to be round so you could just cut off pieces of a dowel or any strip of wood for that matter.