Useful apps for the trail
NZ Tide Times: Timetable for tides around the coast of all New Zealand. Works offline, great for all the tracks that require low tide to walk through.
Osmand: Similar to Google Maps, but you are able to download all of the maps of New Zealand for offline use. Works with .gpx Files as well. Note that these are Flat Maps and not Topograpghical maps - they don't show elevation or small streams.
AlpineQuest with Offline Topo maps: A step by step manual how to download and import Topo Maps into AlpineQuest. Didn't try this.
Back country navigator: Fully featured topo map application. Topo maps for New Zealand can be downloaded inside application for free.