For smaller stickers and die cuts, use a recipe box with tabbed dividers. This system also works well for die cuts organized by theme. The box is small enough that it can be packed with essentials and taken to a crop.Corkboard: Hardware Drawers:
Take a walk down the storage aisle of any hardware store and you'll see multiple storage options. My personal favorite is a unit that contains little drawers with clear fronts, but there are many different sizes and styles to choose from. A simple label attached to the drawer front identifies the contents. This is a great storage solution if you decide to cut up your letter stickers; use the drawers to separate different styles and sizes of each letter.