Ask the bartender what they drink after close. Order that.

Bartenders spend all night building other people's drinks; what they pour themselves once the doors are locked is a different menu entirely. Find a bar where the person mixing is close enough to talk to, sit at the counter, and when there's a lull, ask what they drink after close. Order it — alcoholic or not — and get the reason it's the one. Half the time it's a cold lager; the reason it's that lager is the part you came for.