I will file this under organization...I guess that is a good fit.
This may seem silly, and maybe ya'll already know...but trays are awesome. I love using trays to help distribute materials quickly, and to get clean-up going faster. I picked up some really great trays (the one the the left is that last one) from a Dollar General when I taught K-2 Art in Greenville, NC. The trays were especially helpful in the elementary classroom when time and efficiency is of the essence. I learned then to keep at least two trays of water cups ready at all times so I was always ready to paint.