I bought a two-sided plastic pencil box sort of thing at the dollar store. It has several compartments on one side, I think for erasers, paperclips, etc. The other side has one long compartment for pencils and pens, and 2 half size of that.
I keep my empty bobbins in the long compartment. My filled bobbins sorted by color go in the side with several sections. Each section holds 5 or 6 easily. In the half size sections, I keep random bobbins with just one color on each, and I use those up when I am piecing.