Marleneann it depends on how much soda you drink
My wife does not drink alcohol,but lots of soda..
so she Always purchase one.She drinks Sprite Zero,and
that is what Carnival has,as well as diet coke.
One problem though is you may have to walk up to one of
the bars to get your sodas(the bar waiters do not like bringing
you a soda where you are sitting,unless someone is also ordering
a pay beverage.Overall it is a good buy.
Hope this helps..any more questions...ask away!