"zac" is six pence or five cents in Australian slang. People who are crippled with arthritis and walk around bent over are commonly called "Zac"; they look like they are searching for a coin they dropped.
"I just got divorced, Hoppy. The bloody moll took the house, the kids and every zac I had. I'm doing it tough, mate, don't you worry about that." - 'Robert Barrett, 'Between the Devlin and the Deep Blue Seas'.