...and tries to buy a drink.
QUARK: Well then, you have my sympathies and the first round of drinks is on the house.
QUARK: No. It's a figure of speech.
If Quark charges customers at his bar -- even though I've never seen Quark collect money at the bar, he has been known to count gold-pressed latinum after hours (The House of Quark, Season 3, Episode 3) -- how do the Starfleet officers drink?
If the United Federation of Planets (officially) has no currency, what do they pay for their drinks with?