I flew Air NZ on three flights last month. If you have a wheeled suitcase, just plan to check it. The carry-on needs to be 7kg or under. There are scales in the baggage area so you could weigh your carry-on items to make sure they complied. They don’t charge to check your bag and I saw very very few wheeled bags being brought on the three flights that I took. My first flight was part of a group tour and our tour guide advised us upfront of the weight restrictions and that we would need to check bags.
My carry-on item was a daypack and my personal item was a purse. Air NZ did not weigh my carry on bags, but it was pretty obvious that mine were under 7kg. I had packed the daypack with a change of clothes, electronics, 3-1-1 bag, etc. and it weighed about 4kg.
A few more things about NZ airports:
I got pulled aside at security checkpoints in both Wellington and Auckland for things that have never been an issue in any other airport:
1) Do not pack any batteries (even AA or AAA) in your checked bag. Any spare batteries in your carry-on either need to be taped together or stored separately. I had packed 2 spare AA batteries and 2 AAA batteries in a ziploc bag in my carry-on. I got pulled aside in security and they told me it was allowable to have the spare batteries, but they could not be “loose” because the nodes might touch and start a fire (these were not lithium batteries). Anyway, the security guy put them all in different places in my carry-on (e.g., 1 in the toiletry bag, 1 in a packing cube, etc.). They also inspected every item that had batteries installed. I had a battery-operated electric toothbrush and noise cancelling headphones.
2) Security saw a tube of sunscreen in my 3-1-1 bag that got flagged. It was under 100 ml so it was ok, but it seemed at least half the bags ahead of me were getting pulled for screening and they usually seemed to be closely inspecting the contents of people’s 3-1-1 bags. Don’t be alarmed if your carry-on gets selected for extra screening.
It took me an hour and fifteen minutes to get through passport control and security at Auckland when flying back to the U.S. I don’t know if that is normal or whether there was an issue on the day I flew back. I flew on Feb 28th.