The great thing about ribollita Italian bean soup is you can add whatever you like to it. Start with a chicken broth (or vegetable broth if you prefer) and then you can use the veggies suggested in the recipe or else choose your own. Anything goes in this Tuscan bean soup really, including spinach, mushrooms, zucchini, and peas. Sweet potato, white potato or yam will also add flavour but bear in mind these are starchy ingredients which can thicken the soup and, if you're also using bread, it might end up too thick. This isn't an issue since you can always just add extra broth, but it's worth knowing. Oh and I imagine seasonal favourites like pumpkin or rutabaga would also be good. In fact all kinds of vegetables work in this tasty white bean kale soup!