Green’s Dictionary of Slang

buying alcohol legally, and then taking it to a teetotal or ‘dry’ area of the country for consumption.

1910		Truth (Wellington) 14 May 5: ‘Kegging,’ i.e., that beastly habit of boozing out of a keg, is peculiarly a New Zealand habit [DNZE].
1976		(ref. to 1906) M.H. Holcroft Old Invercargill 112: In August [1906, two months after no license had been carried] a new social phenomenon made its appearance. Two parties of young men […] bought a keg of beer from the depot outside the town boundary ‘and straightaway consumed its contents’ [...] This may have been the first recorded instance of ‘kegging’, a form of public drinking which for a long time seemed to be peculiar to Invercargill [DNZE].