We did fairly well on JetStar SYD-CNS-SYD over the summer. I agree with the "be well informed" caveat, but we had no issues. I think non-bottled water might actually be free - or my wife just talked her way into it, but yes all other "snacks" and drinks are pay. The "with luggage" fare was maybe $20 AUD more than the without for us, my only gripe was the website wouldn't let me buy 2 tix w/ and 2 w/o on the same itinerary, so I ended up with 4tix w/ rather than hassle - and we needed only 2 pcs of luggage as expected.

I did see some folks being hassled over carryon - which legitimately did NOT fit (by a large amount), and while I don't recall the specifics, it seemed to uniformly be a single ethnic group....so a huge YMMV there. We had small softside backpacks (not the huge hiking things) which, with coats inside, would have been too thick for "the box" but weren't even asked to try to fit them. My other guess was pax who paid for luggage weren't hassled about possibly borderline carryons where ones who didn't were closely scrutinized. Since we neither fit the ethnic nor "no luggage" groups, I never determined.

I didn't see a good way SYD-CNS that got us anything useful in the way of frequent flier benefits in the USA - Quantas fares were 50-100% higher than JetStar - and we don't do much on American these days anyway. NZ would have been excruciating and taken a whole day since they don't go direct SYD to CNS, but only through one of two cities actually *IN* NZ

I assume from the OP that s/he does NOT need to be in SYD/MEL just CNS, so the NZ or Quantas US-AUS approach might be best. I'll agree that SYD-CNS was a pretty comfortable flight and that a window seat is a bargain - the r/t JetStar ticket wasn't much more than a 15-20min reef overflight would have cost, and I got some beautiful pictures out the window!

HTH,
Richard