Warnog is a Klingon alcoholic beverage, not quite as ceremonial or popular as bloodwine.

Warnog was available at O'Dell's bar in the Aneher II neutral zone between the Federation and Klingon encampments.

In December of 2267, after imbibing a large amount of warnog, K'Vak got into a bar brawl with other drunk Ronald Saygar. (TOS novel: The Case of the Colonist's Corpse)

Worf and General Martok drank warnog while the IKS Rotarran was escorting a Klingon convoy to Donatu V in 2374. (DS9 episode: "Sons and Daughters"; DS9 novelization: Call to Arms...)

In 2379 when Worf was lying in wait in order to blackmail Councillor Kopek into turning over his personal codes allowing him to access Klingon fleet command, Worf could smell warnog on Kopek's breath as he entered his office.

Martok, Chancellor of the High Council of the Klingon Empire, kept a well-stocked liquor cabinet in his office containing both ale and warnog. He was drinking warnog as he was trying to figure out how to punish Worf for stealing the Klingon fleet's command codes to give to the USS Enterprise-E. (TNG novel: A Time to Kill)