The poster says today only but it's been up for a couple of weeks now.
Basically, for $3 extra with any burrito you get a regular mexicrinkles, a can of drink and a dipping sauce. A meal is usually $4.50 or so extra and the sauce is about $1 I think.
Only seems to be available at Tea Tree Plaza, it's not at Marion or Rundle Place that I've seen.
how much is a Burrito?