Tram from Airport to Florence, For tap and Go Payment Option how do you pay for extra luggage

We will be visiting Florence in less than two weeks and plan to take the Tram to Santa Maria Novella Station. You have to pay extra for "large" suticases. If you are using tap and go (no paper ticket) do you have to use a different credit card for each suitcase? , Or is it better just to buy paper tickets for the luggage.