...in case anyone wants to go back and look at the various theories on this.
I hear what you're saying, M/U, but I think the evidence actually points to
Frodo's old clothes.
The exact wording in "The Black Gate Opens" is actually: "the coat of mithril
mail that Frodo had worn wrapped in his tattered garments." And in "The
Field of Cormallen" Gandalf says they will wear the same clothes they wore "on
their way to Mordor" not "in Mordor."
Sam, of course, had been wearing his old clothes beneath the Orc armour the
whole time.
It *is* ambiguous, and I admit I also thought they wore the Orc-rags to the
ceremony until I read the text a little closer along with all the excellent
answers in the thread
below