Getting in
Most visitors from visa-waiver countries (including the US, UK, EU and Canada) need a New Zealand Electronic Travel Authority (NZeTA) before boarding their flight, applied for online in advance — it isn't issued on arrival. An International Visitor Conservation and Tourism Levy is charged alongside it for most travellers. Border biosecurity checks are strict: New Zealand's economy and ecosystems depend heavily on keeping out foreign pests and diseases, so declare any food, outdoor gear, or camping equipment on arrival rather than risk a fine.
Money and costs
The currency is the New Zealand Dollar (NZD) on both islands — there's no separate currency or exchange step when crossing the Cook Strait. Card payments, including contactless, are accepted almost everywhere, even in small towns. Tipping isn't expected or customary anywhere in the country, which keeps day-to-day costs more predictable than in tipping-culture destinations.
Driving
New Zealand drives on the left, same convention as the UK and Australia. Distances on a map can be deceptive — winding roads through hill country mean actual driving times are often significantly longer than the kilometres suggest, especially on the South Island's mountain routes. A rental car or campervan is the practical way to see either island properly; public transport between smaller towns is limited.
Ferries between the islands
The Interislander and Bluebridge ferries both cross the Cook Strait between Wellington (North Island) and Picton (South Island), a crossing of roughly three to three and a half hours. Both car-carrying and foot-passenger tickets are available, and the crossing itself — through the Marlborough Sounds on the South Island side — is scenic enough to be worth doing in daylight rather than treating it as a formality.
When "summer" and "winter" actually are
Seasons run opposite to the Northern Hemisphere: December through February is summer, June through August is winter. This matters for packing and for what's realistically open — some South Island alpine passes and hiking tracks are seasonal, and ski fields only operate in winter. See Best Time to Visit for a fuller month-by-month picture.
One island or both — the practical version
If time is under two weeks, this guide's honest advice (see How to Decide) is to properly commit to one island rather than rush both. If there's more time, splitting the trip using the Cook Strait ferry or a short domestic flight between Auckland/Wellington and Christchurch/Queenstown is completely standard — full sample itineraries are on the itineraries page.