Try paper grocery bags. Shine a strong light source on them from an angle like
10 or 2 o'clock. The light plays upon the bags to create interesting shaped
& the translucecy of the bags gives some nice middletones. Have some standing,
folded, laying down in a still life set up. Have students tackle the project
by drawing the shadow shapes. We did this in college. It is challenging &
helps students learn to discern shapes.
Plastic bags would probably be interesting too...Bill in NC