If I had the space I'd be a happy camper! I would use it to create and store all my non-food experiments - homemade soaps, lotions, essential oils, packaging supplies and random ingredients
Maybe you have a hobby or are interested in one where the space would be useful for you?
If you live somewhere warm, you could also use it seasonally as a kitchen to keep your house cool, or to expand on more kitchen projects you don't have room for. Would be great to have an induction burner, crockpot, dehydrator....