Casual wear such as a pair of jeans and a sports shirt are acceptable at casual restaurants and pubs at night. Just don’t wear thongs (flip flops) work boots or go shoeless. Of course upmarket restaurants require a reasonable standard of dress.
Don't overdress. The Aussies have a pretty relaxed dress code- long trousers in the evening (blokes) will get you just about anywhere (trainers are fine). Doris' can and will (always) dress up in what they like.