I, of course, believe the opposite. :) But on the Deuterocanonical books I would like to ask what specific and Uniquely Catholic (or Apostolic) beliefs are found there, but not in what I consider to be scripture? To my knowledge, purgatory is one, but the Orthodox reject that, as we do. (I think they sort of meet you half way, though. :) I can't recall the Orthodox distinction.) Anyway, my working belief has been that the Deuts really do not go a long way in defining our differences because you guys almost never quote them to me. You will quote the Fathers and you will quote what I call scripture, and you will quote the Catechism, but there is almost nothing from the Deuts. I just ask myself: why is that?
The short answer is, because it is no authority to you, and would not define the Catholic views with precision as the Catechism does.
Off the top of my head, among the Deuterocanonicals we find the clearest textproof for prayers for the dead (for the Purgatiory itself we are fine with 1 Corinthians 3), the freedom of will (Sirach 15:14), the concept of the communion of saints, guardian angel, demonic possession and exorcism in Tobias.