Waterproof as clients should have the option of adding water. A wet sand tray is a whole different experience than a dry one. A lot of sand tray therapists have two, wet and dry. As for a small box for figures, once you start collecting miniatures most find it very addictive and even my basic kit has about 6 boxes worth which I add to all the time. A proper sand tray therapist will have shelves and shelves worth. I love how they look at set out. It seems full of endless possibilities and the child in me gets really excited.