Cut the plastic milk container in half lengthwise. It is important that you have the handle centered on one of the halves, as the handle will serve as the nose of your mask. Discard the other half as you will only be using the half with the handle.
Decide if the mask will have cut-out or painted-on eyes. If eyes will be cut out, trace their shape with a marker and cut with a utility knife. The eyes should be on either side of the handle, as the handle will be serving as a form for the nose.
Mix a papier-mâché paste by combining 1 cup of flour, 1 teaspoon of salt and 2 cups of lukewarm water. Mix until all lumps are dissolved.
Shred the newspaper into 2-inch-wide strips. If the strips are longer than about 3 inches long, cut them, as smaller sections are more suited for this project.
Layer the back side of the mask with the newspaper strips, first covering each strip with the papier-mâché paste. Work in one direction and cover the entire back of the mask. Turn over the mask and repeat on the front.
Repeat the newspaper application, this time going in the cross direction. For maximum durability, consider three layers of newspaper, though two will be sufficient.
Allow the mask to dry completely. Put it in the sun or in the oven at the lowest setting and check after one hour.
Paint the mask white. Expect to use two coats. Once the white paint is completely dry, embellish with facial features. Make sure you use acrylic paints. You can use spray paint for the white coat, but you will need a detail brush for the facial features. A google image search for "kitsune" will give you an idea of the variations commonly used for decorating the mask.