Empty space below a staircase could be transformed into storage by adding shelves. Since stairs are typically pretty wide, the shelves you add in this area can be very deep.
You can store multiple items on each shelf under a staircase, and since the space below the staircase is usually cramped, it’s a great way to make the most out of this unused area.
While cabinets may be used underneath the kitchen island, you could also add open shelves around it to include more space for storing dishes, books, decorations, and other items.