I know it may sound funny, but I have a huge tackle box. I mean BIG. When it's opened, there are actual trays that you can take out one at a time, about 25 squares in each, each square 3X3 in., and of course, with a lid. (Think of a bead organizer, the big 'box' type with all of the compartments. There are a total off 6 large trays for my assortments of clay/colors. Then I have a big spacious portion on the top of the tackle box for my sculpting tools and other things. Best thing, the clay doesn't stick to any of the plastic, so I can always rearrange as I please :D
It works great for me since I travel around and make my items at parks here and there :) The tackle box is about 3 feet long, 1.5 ft in with, and 1.5 in H.