Green’s Dictionary of Slang

(Anglo-Irish) an alcoholic drink; usu. in phr. will you have a sniffler?

1849		H.A. Wise Los Gringos 378: I’d get up early and take a good sniffler of brandy, with a dash of peppermint.
1937–84		Partridge DSUE (1984) 1103/1: [...] 1935.