I found these chip and dip plastic trays at Dollar tree and I heard the angels sing. I made 4 trays (1 tray per group) with enough materials for 5 students. They stack beautifully on top of my cabinet when not in use out of reach from little hands. Of course, I had to train my students to "not touch" and "one at a time", but it's working like a charm!
Blessings to you,