Green’s Dictionary of Slang

(N.Z.) to take charge of; to get ready.

1988		McGill Dict. of Kiwi Sl. 62/1: jack [...] to organise or prepare; eg ‘I’ll leave you to jack this crew, Jill, and I’ll take the rest.’.
2003		McGill Reed Dict. of N.Z. Sl. [as cit. 1988].