You need a milk jug that has is washed, dried, and has the cap and all labels all removed from it. Simply draw faces on the cartons with a sharpie marker.
Next, use an craft knife to cut a small opening on the side opposite your face. You need it big enough to fit your light inside. For safety reasons, we used battery operated flickering tea lights (thanks Mandie for the suggestion!) instead of candles.
You can't tell from this picture, but they do shine really well at night. We put them out for our neighborhood Fall Festival last weekend, and will put them out again for Halloween night.