Relating to Australianism, what is "fair suck of the sav!"?

Used to inform somebody that they’re taking more than their share, etc.

http://en.wiktionary.org/wiki/fair_suck_of_the_sav

It can also mean

exclamation of wonder, awe, disbelief

example

Man 1: "Pie and sauce thanks mate"

Man 2: "That'll be seven bucks"

Man 1: "Fair suck of the sav!"

eg 'You've got to be kidding'.

http://www.urbandictionary.com/define.php?term=Fair%20Suck%20of%20the%20Sav

Just as a point of interest - a sav is referring to a saveloy. You will sometimes here this expression used as "Fair suck of the sausage."

A saveloy is a type of highly seasoned pork sausage, usually bright red in colour, which is served in Southern English fish and chip shops, sometimes fried in batter. The word comes from the French cervelas, a pork sausage, at one time sometimes made from pigs' brains.

The saveloy is available in Australia, usually battered and known as a "battered sav".

https://en.wikipedia.org/wiki/Saveloy