Plaster of Paris, watercolor paints, and plaster molds can be purchased rather inexpensively at craft stores for this unique activity. Encourage your youth group to get creative, by hosting a Plaster Party at your church, or in your home... You can advertise the event with posters that say "Get Plastered!" and possibly charge a small admission to help cover the costs. Teens will design and paint their own plaster molds, and you can encourage creativity with 'best looking', 'most colorful', 'most retro-design', 'worst eye-sore design', etc. awards....
A good spiritual discussion would be "Created In God's Image: What does it mean?" or "You Are Fearfully and Wonderfully Made" or "Designed For Good Works In Christ"