This recipe uses chopped chocolate and peanut butter cups. Technically, you don't need any mix-ins since the ice cream base flavor is chocolate peanut butter. However, I love the texture and flavor that the mix-ins add ensuring that you get peanut butter chunks in every bite. You can also use chocolate chips, chocolate chunks, peanut butter chips, peanut butter nuggets, chopped gluten-free Oreo cookies, toffee bits, and chocolate fudge swirls.