Umm, got this from the Jetstar website:
Passengers are also welcome to bring their own food on board however please note that there will be no refrigeration facilities or any heating facilities on board and crew will not provide cutlery, napkins or cups for food brought on board by passengers.
I've done it several times already - on JQ longhaul, I find a footlong subway purchased just before departure is more filling, more tasty and far cheaper than paying for the meal onboard!