Land Down Under
Alright, before I start, there is something you need to know about Australian slang.
50% of it is made up on the spot. So if you ask where the saying originated from, it's most likely that we can't tell you. There are 3 categories of slang. The shortened slang, replacement slang and long slang. Shortened slang is where we try to make life easier by shortening words. Replacement slang is made-up words used to replace normal words. Long slang is where we make life harder for ourselves because... well, we can.
These aren't all, but the most common.
Good luck...
Shortened
Arvo [Ah-voh]: Afternoon
S'Arvo [S-Ah-voh]: This afternoon
Barbie [Bah-bee]: Barbeque
Brekky [Breh-key]: Breakfast
Brolly [Bro-lee]: Umbrella
Chrissy [Chris-ee]: Christmas
Ciggy [Sig-ee]: Cigarette
Defo [Deaf-oh]: Definitely
Devo [Dev-oh]: Devestated
Flannie [Flann-ee]: Flanelette shirt
Mozzie [Mozz-ee]: Mosquito
Servo [Serve-oh]: Service station
Replacement
Billy [Bill-ee]: Tea pot/Kettle
Ankle Biter: Child
Bogan: Like a hill billy
Bush: Outback/Middle of nowhere
The sticks: Outback/Middle of nowhere
Crikey: An exclamation of suprise/shock
G'Day: A shortened version of 'Good Day' but it means 'Hello'
Dag: Nerd/Geek
Drongo: Idiot
Iffy: Risky/dodgey
Knickers: Female underwear
Lollies: Candy/Sweets
Ripper: Fantastic/excellent
Sneakers/Joggers: running shoes
Stiffy: An erection
U-ee [Yew-ee]: A u-turn
Long Slang
AccaDacca: ACDC (the band)
A cold one: A beer
Bloody oath: an exclamation of frustration/shock
Choccy Bikkie: Chocolate buiscuit
Take the piss out of: Mock
Crack the sh*ts: Get angry
Good'on ya: Good job
Stubby Holder: Beer holder.