Your students will think that these penguin projects are "COOL!" Use water bottles, cotton balls, wiggly eyes, and construction paper to create these cute winter penguins. Using a strong glue, you c (Water Bottle Projects)
How to make a Sub-Irrigated Planter. I'm not sure I would use a two liter plastic bottle though. Over time I would fear the plastic breaking down enough to poison the plant. Perhaps a wine bottle instead.
Self-watering planter. Cut top third off bottle. Drill small hole in cap. Pass string thru hole. Fill bottom of bottle about halfway with water. Place top upside-down in bottom and put plant in. String will wick up water.
DIY Tiny Sumo Bowling Pins for Kids, made from recycled plastic bottles - ewe on the sumo; but a nice cheap way to make a bowling set for toddlers. For whatever reason bowling sets are always a favorite.