Staying connected to Internet while travelling in New Zealand cannot be easier these days. You can bring and use your own country's GSM card but this will be charged with hefty bill even on low data usage.
Hoping for free wifi may be an option, but this only available in fast-food restaurants (MacDonald's) and public space in big cities. When you hit the rural road, this will be non-existent.
The better option is to purchase local NZ GSM card. After doing some research, I found that there are prepaid cards available for foreigners to use, then I put my choice on XT by NZ Telecom. Which I later can say that this is the best prepaid SIM in New Zealand can offer for tourists.