Organize For the Season - Now that you know what's staying in your shed, you must consider when you use the items. You don't want to move a stack of gardening tools just to get to the snow shovels you'll need in the winter. If possible, dedicate one side of the shed to warm-weather specific equipment and the other to cold-weather equipment. This will alleviate any confusion on where items are and save yourself plenty of time when working.
Buying an outdoor storage building with a loft greatly increases storage capability, allowing you to store rarely used supplies overhead. For the exterior, build your own lean-to and attach it to the outdoor storage building to form a sheltered area for firewood.