To form the handle in the center divider section of the box, mark the ends of the handle and drill a suitable size hole for both ends of the handle. Drill more holes evenly across between the first holes to open up a slot for the handle of the box.
Use a craft knife to cut between the holes (without splitting the wood) and clear away a rough slot between the holes on either end of the handle.
Use round and pillar (flat) files to smooth away the inside of the handle slot or oval. If you do not have files, roll sandpaper up into a fine roll, or make a tiny sanding block using a round toothpick or a wooden stir stick. Use these to sand the inside of the handle until it is straight and even, with rounded ends.