I added various transparent and translucent plastic items (bubble wrap, bottles and caps, jewel cases, etc) from the recycle room to the light table along with markers.
I let the children draw as they saw fit.
Here are some of their creations displayed in the nearby window:
Ms. Erin: What do they remind you of?
K: Car lights, all day long. A bowl.
M: These are water bottles.
K: Look, a button!
A: This is for my mommy.
B: I made this for your baby, Ms. Erin.