Doesn't matter where you are in NZ, EFTPOS (electronic) transactions will almost certainly be accepted. If you have problems it's almost always your card issuer, not the retailer. Personally, I don't bother taking cash, arrive and get ~$100 in cash from an ATM for incidentals, and then everything else goes on cards. Only thing to be aware of is that touristy places have started "offering" to convert into home currency - and as always, the rate is horrible. Just charge in NZ$ IMO.