Our whole language in Australia is basically slang, but here are some of my favorites that I often use:
Buckley's – equivalent to a snowball’s chance in hell
“You’ve got Buckley’s of that happening.”
Two chances – Buckley’s and something less likely than Buckley’s
“I’ve got two chances to pass this exam.”
Cactus - dead, broken
“My car is cactus.”
Furphy – a rumour or a bold lie
“That story about John catching a 25kg Barra was a furphy.”
Iffy – questionable, dodgy
“That repair is iffy.”
Silly as a two bob watch - Intellectually deficient
“Mick is as silly as a two bob watch.”
Sparrow’s fart – dawn
“I have to get up at sparrow fart tomorrow.”
Bag of fruit – suit
“I’m absolutely melting in this bag of fruit.”
Shank’s pony – walking somewhere
“If you can’t afford a taxi, take Shank’s pony.”