I hope a bit of advertising is OK, but there is a chapter in my book
Mountain Fever that covers a hike around lake sumner and Mt Cook including alot of info on the plants, history and uses (can't reccommend it enough!!!). There is also some photos in the gallery but these are mostly of the hike.
I found that flora can change between valleys and there are alot of fiberous plants, some of a larger version to our native ones and because of the countrys isolation, there are many that are not found any where else.
I did not go as much into the plants they used for food as I did about the ones they used for shelter clothing, etc, but the flax is used alot and in comparison is similar to our nettle. Shells, feathers and bird bone were also used (birds being mostly large ground dwelling - due to no large preditors) especially from the 10 foot tall Moa, when it lived.
Over all the country is unique for its plants and trees - many are just amazing, especially if you see them at the right time. You may have to be careful what you use for bushcraft reason as I found, rightly so, that the ziwis are very protective of this environment and will not allow any thing taken out or brought in (I had pre-packed/mixed all my food for the hiking, as I usually do and it was all taken away)
. Apart from that, there are plenty of isolated places you can go and do your own thing, any map will show hundreds of hut/cabins in various places, but off the beaten track these may be owned/used by hunters. After a bad rainfall rivers are normally safe after two hours - do not try to cross during a storm and as a added bonus, there are a few hot springs out in the hills, just wear trunks to be on the safe side.
There is lots more I could say, but I gareentte that you will get alot more out of the trip by not knowing alot about the area beforehand (I know what I mean if no one else does!!!)