We flew to Cairns via Brisbane with DS when he was 10weeks old and he was fine. He fed on take off and landing and generally slept the rest of the time. We just packed normal nappy bag stuff (however airlines will allow you an extra cabin luggage bag for baby's needs)

I've also flown with him to Melbourne by myself when he was 8months and again he was okay. He was a bit more fidgety, but I only needed to feed on landing (apparently take off isn't as bad on their ears). I just took some toys and a book to keep him occupied.

On all flights, we had a spare seat next to us which was helpful if I needed to put bub down, or lay him down when he fell asleep after our flight got delayed by 1.5hrs.

Good luck and enjoy the holiday