Placing the stem of the pop mold in the mouth of an empty carbonated beverage can will keep it upright will you fill and freeze it. Plunging the stems into a thick block of white polystyrene foam works, too.
Mix and match your favorite flavors! The sky is the limit when it comes to these pops. Just remember to either fill your pop containers with the densest mixtures at the bottom, or freeze each layer solid before topping it with the next.