If you pick up a copy of The City News there is a voucher in there for $3 off food purchase from most of the participating vendors in the Wintergarden.
So you could buy a $4 burger and pay $1 + voucher.
Guys at work here are raiding the newspapers (free street press).
Sorry have not a voucher to place on the site but it's pretty noticable in the paper.
Where are the City News papers normally found? I'm not in the city too often.
Also, there are online versions of the paper, so I'm not sure if they would be valid but there doesn't seem to be anything to the contrary, so the link is below.
http://paper.questnews.com.au/QST_BCN/bcn006.pdf