@Bart Lewandowski,
Can you provide detail on how you even got the ShoppingCartCustomData to store the information you wanted it to store? We're working on something similar but haven't yet been able to access this custom data property correctly. Honestly, not even sure where to begin. We know it's there but no webpart exists to add it or that contains the field. We are looking to build an internal company store and simply want to capture an employee number.
Thanks!