I got this idea from the Family Fun Magazine. It was so easy to do and they turned out great. The kids loved it!
A clear dry jar
Orange acrylic paint
You take the masking tape and cut out jack-o'-lantern pieces. You tape them on the jar and then let the kids go. They can put as much orange paint on the outside of the jar as they want. When it dries, you remove the tape and put a light in. Simple as that!