Any size milk jug will work to make milk jug ghosts. This milk jug ghosts tutorial uses a gallon milk jug, but a half gallon one would work too. And any type of plastic milk jug, either clear or white, will work for this craft. And if you don't have one, you can actually order plastic milk jugs online. You can use glass milk bottles to make Halloween milk bottle ghosts too. And actually, if you do that, you should be able to wipe the paint off after Halloween and reuse those bottles for something else. Milk cartons that are made from paper aren't ideal for this because they're completely printed on. So, you'd need to paint the entire carton white first. Which, you can do if you really needed to, but then it's a completely different craft.