Green’s Dictionary of Slang

sugar, esp. when added to a hot alcoholic drink.

1839		C.J. Lever Harry Lorrequer 44: ‘Hand his lordship over the groceries’. — Thus he designated a square decanter, containing about two quarts of whisky, and a bowl heaped high with sugar .
1841		Lytton Night and Morning v. Ch. ii: A private room and a pint of brandy, my dear. Hot water and lots of the grocery .