Different solutions depend on what you'll be storing in this space. Hooks (even temporary adhesive ones) may provide options on the walls on either side, and you could adhere magazine holders for additional storage of cleaning products, kitchen supplies, etc. Wire shelving has its positives, in that you can use S hangers to suspend items in space that may otherwise be unused! However, be careful when storing things like books, as they could be slightly damaged or fall through the cracks. (You can use tiles or any other large, flat surface to avoid this.)

If you're storing a lot of linens and clothes that you don't normally use, vacuum-sealed packing can help to reduce the bulk. Additionally, if you want to store a surplus of small and medium items, you may want to purchase stand-up shelving to double the surface area.

Best of luck!

If you will be stacking items on the shelves, then I think the fact that they are pretty far apart might create a problem. Whether they are towels, jeans, photos, gift wrap or craft supplies, you need some type of way to break up the space vertically, so that you can get to what is on the bottom as easily as what is toward the top of each shelf. Adding another shelf might help. You might also get some plastic bins with lids for the seldom-use items, label them, and store them on the top shelf. Good luck to you.