Dull pins/used needles. I have a bag I put thread snippets in and drape them over bushes in the spring for birds' nests. It's fun to see the colored bits in their nests. I also have a flat rate box that I put small scraps/batting into. When it's full, I post here for those who make pet beds. I save selvages. Eventually I want to cover the cushion on my sewing stool. Empty thread spools go into plastic recycling. I try to recycle as much as possible.
OK, Holice, what do you throw away? We're waiting to hear.