If they are semi transparent you can make garden lights out of them using Christmas lights.
Yoplait containers are great for kids' art stuff - like a set of crayons for each kid or little dollops of paint - because they have a wide base and don't tip easily.
I am also thinking of the energy drink bottles...so here's what I came up with...drill a hole through the cap and bottle (horizontally) and remove the cap. Cut off the bottom of the bottle (thinking petal-like) and insert a tiny LED bulb. I think a string of these (painted or not) would be cute...