Pick a spray paint color that matches the rest of your decor. Place the milk crate in an open area and cover it with spray paint. Allow to dry according to the label recommendations.
Set the milk crate with the open end facing down and mark the corner edges where you need to drill. Pick the similar solid spot on all four corners.
Use the power drill to create screw holes at each place you marked. Keep the drill bit perpendicular to the plane of the crate as you drill.
Measure the length and width of the crate. Use these measurements to mark the plywood sheet and cut it to fit with a saw. Rub sandpaper along the cut edges of the plywood to smooth it.
Measure the locations of the drill marks on the crate in relation to the corners of the crate and use these measurements to mark the drill locations on the plywood sheet.
Drill screw holes in the plywood. Place the plywood on top of the crate, matching up the corner holes. Insert the screws into the top of the plywood and screw them in to attach it to the crate.