The Grand Nagus carries with him a staff that is traditional for an individual to kiss the head of after receiving advice from the Ferengi leader. The Grand Nagus possesses the ability to appoint a Grand Proxy to act in matters in which he is unwilling or unable, and he might also travel with the cane as proof of authority given from the Grand Nagus. The staff can be seen in several Deep Space Nine episodes, such as 'Rules of Accuisition', 'Profit and Lace', and Voyager 'False Profits'. There were many staffs made during the the production of the show (perhaps as many as 15), and this is one of them.
I realize this is not a costume, but I feel it is an important part of the Grand Nagus character and costume, so I have included it here.