I use small 7.5" x 4.5" x 2.5" white boxes that my wife gets from the trash at work. I label the outside of the box with the number of the mold so I can look at the stack and pull the box that I need for my biuld that day. I used to use ziplocks, but it is so much easier to find what you want when the boxes are stacked neatly and you can see the labels on the side.