A small cable spool, probably for wire or ethernet.
Cable and wires are notorious for the invisible "elves" that tie complex, mathematical knots when simply crammed into a container. To resolve this debacle, cable spools that allow the cable to be coiled around it like a snake were invented. Spools come in different sizes depending on the wire, and are made of wood, plastic, or metal. Discarded wood spools are also used by some college students and cheapskates as impromptu tables.
Found in construction sites, hardware stores, and college dorms.