Polymer clay (Sculpey)
Polymer clay is so versatile - it can be shaped and reshaped a multitude of times without deterioration. As long as it is stored away from excessive heat and direct sunlight, polymer clay can sit unused for years and still be workable (though it may require softening additives if left for very long - baby oil works well).
Unlike earthen clay, it doesn't have to be fired in a kiln, nor will it dry out at room temperature. Polymer clay cures at significantly low temperatures tin a home oven or toaster oven. Most polymer clay must be cured at 130°C for at least 15 minutes per ¼ inch (6mm) of thickness. If your piece is delicate try making it a little house of foil, placing it on a ceramic tile and leaving it in the oven while it cools to try and reduce the thermal shock of taking it straight out.