For a town this size and this remote, the food in Coober Pedy is better than you would expect. The mining community is genuinely multicultural — Greek, Croatian, Italian, Serbian, Chinese, and Aboriginal — and that diversity shows up on the menus.
The cluster of restaurants on Hutchison Street is the obvious place to look: a couple of Greek-Italian taverns, a Chinese restaurant, the bar at the Desert Cave Hotel doing Australian pub classics, and a string of takeaway options. Don't expect anything fancy. Stock up on supplies at the IGA on the same street if you are driving on.