In Economy, a single snack is offered. Some of the latest snacks they've offered have included small trail mix packs, fergy's chocolate orange shortbread cookies and the snack I was offered today was Kez's Kitchen baked bikkie bites salted caramel and white chocolate.
The snack is offered with either water (large NU brand bottles poured into individual cups), apple or orange juice (just juice brand).
There is currently no buy on board menu so if you're not happy with the above options then I suggest you BYO however it's worth noting that BYO alcohol is obviously not ok.
In Business Class things are slightly better. In addition to the same snack as economy, those in business get a snack box which has a muffin/brownie type thing (this changes), a couple of packets of chips, rellish and a choclate. The drinks served in business class also expands to soft drinks (coke/sprite etc), wine (one white and one red) plus beer (today this was a four pines summer ale).
Whilst not applicable to the original question, If flying Virgin Australia Regional Airlines onboard an A320 or F100, depending on the flight length the food is even more substantial. Last week I flew out to Christmas Island onboard the A320 and a sandwich was offered both ways in a box along with a couple of chocolates. On the way over it was a choice of pastrami or vegetarian sandwich and the way back was a single option of chicken. In addition, drinks offered included water, tea, coffee, juice, and soft drinks (but no beer or wine).