This is the sacred cup, the thing all the Grail legends were really about. It symbolizes the Goddess, because the cup is like a womb; it's the right basic shape, and good things flow out of it. As such, it also symbolizes nurturing energy, and the cup of life that never runs dry. It's attuned to the element of Water.
On a practical level, it's used to hold the wine (or Not Wine, as the case may be.) This one is a wooden goblet; but any kind of cup, made of any kind of material, will do. Like the other things here, it's the idea behind the symbol that counts, but the esthetics are pleasing. And if you aren't willing to get nice things for the Gods, who can you get nice things for?