Shannon had the good idea of posting your favorite conservation tool here.
I have two. One is my fid. I believe it's a leather working tool; I bought mine at a local Feed and Ranch Supply store in the saddle section. I use it to tighten my sewing and remove pesky staples and misc.
My other favorite tool was hand-made for me by my coworker Kathy. It's a pin tool made from a broken sewing needle set into a nicely sanded stick of ash wood. It helps to have a conservator/woodworker at the library!