glue dollar store tree to lid, fill jar 1/4 of the way with fake snow and 3/4 with water. stick lid on with tree attached, voila! homemade snow globe. cheap and easy, cute christmas gifts. add ribbon or twine onto lid for added effect.
Or several readers have commented that baby oil accomplishes the same thing. Glycerin can be found in the baking aisle of craft supply stores in small bottles. Probably at least 2-3 teaspoons per cup of water.