So with this seasonal event going on you can grab "Festive Mugs" in a city and fill em. the empty mug is not unique, but the full one is. Stack your inventory with empty mugs, fill them all, then relog. all will disappear but one, when that one disappears, its inventory slot with automatically be filled with another. These last after the event ends, and can always be used. This has been in the game for a LONG TIME and its probably in the deep depths of the forums somewhere, but I figured id let all the new guys know how this works since it seems live on retail and classic.
NOTE: Posted in both classic and retail forums so more people can see it and take advantage before the event ends.