I took art foam sheets and made little squares with a set of numbers in one color and a set in a different color for the alphabet. I punched two small holes in each for pinning, and wrote on them with a black sharpie. Now, all I do is either use a straight pin or safety pin to attach them to my blocks in rows and columns. In between uses, they live in two small baggies that are kept near where I am currently using for a design wall (bed, table, floor, etc.) since I don’t have an actual design wall.