A great way to repurpose Styrofoam cups and trays is to use them for arts and crafts. Styrofoam pellets are convenient as a substitute for rocks on the bottom of flower pots to provide aeration and better drainage.
Styrofoam trays with subdivisions are useful as organizers for small arts and crafts supplies, such as buttons or beads. Egg cartons are convenient as seedling starters, and plain trays can serve as canvases for children's paintings or drawings. Cups are readily transformed into pencil holders, and shapes cut out of Styrofoam plates become a beautiful garland when strung together and hung from a balcony or porch.