I encourage my students to recycle and as part of a real world application, I use recycled items in my classroom. I take the cup holder trays I get from McDonalds and place yogurt containers in them. I fill them with paints and use them as paint trays. It's good to leave one container on the tray filled with water so the students can rinse their brushes. The yogurt containers are easy to clean and the trays become nicely decorated!