Visit a local dollar store and purchase low-cost Christmas supplies for two or more teams. Items could include strings of lights, bags, tins, boxes, sacks, or any other Christmas-related things. Purchase some larger items, many smaller.
Divide the supplies among the two teams and invite the teenagers to compete in creating their own Christmas-related sculpture.
In addition to the supplies, also include such items as duct-tape, glue, and string to help in the formation of the sculptures. As prizes, purchase a few other low-cost Christmas gifts for all of your teenagers.