I've only recently got into die cutting this past year and I've just now found a storage solution i like for storing die cut sets.
I took the clear zipper pouch (ziplock bag would work too) that my Brea Reese brushes came in and measured it into three parts. I then used my Project Life Heat Tool to seal the lines to make three separate pouches.
In this one, I have one for my waves set, one for numbers, and then one for leaves.
If you don't have heat tool, you can always use sew it together. But if you're like me and can't sew, you can also use a stapler- just be sure to put packing tape on top on both sides to avoid cutting your fingers. I ended up doing this method in the end because I tend to be rough with things and I have a feeling the heat method wouldn't hold.
Now I have a thin, see through, and easily accessible way of storing all my friends together.