Hi Dawn
I took mainly NZ cash last time (I'm 'old school' and prefer good old fashioned cash!) but when I go back in Feb 2027 I think I'll do half and half.
Most of the 'big ticket' excursions, i.e the helicopters etc, take cards but some of the smaller coffee places and gift shops still prefer cash. I think there was only one place that refused cash, and that was the bar of the hotel in Auckland which insisted on cards or room charging. Everywhere else is much the same as the UK and as the NZ dollar is basically two to the pound, it's really easy to keep a track of prices and how much you are spending.
Happy travels
MLB