Went to New Zealand several years ago, pre garden addiction. I was on the south island. The whole place seems to be a garden. I believe bringing back plants will be a problem. On the bright side I think your dollar will go farther. Highly recommend Milford Sound, and Christchurch is lovely.
Elle

If you are a college student, try to get to Queenstown on the South Island. It is pretty much the adventure activity capital of the place. Lots of stuff for people of any age to do, but a very exciting place full of twenty-somethings. Nice public garden there, too, with a good collection of rampling roses on the fence. Also if you are an experienced backpacker you might want to consider tramping the Milford Sound. They have good accomodations for the self-guided hikers, and that is much less expensive than the guided tours.

This is probably the chance of a lifetime. I envy you getting to see NZ at this point in your life. I found it to be amazingly beautiful, a landscape that will fill your memory for years to come.

NZ is very fussy about species in, species out, so you probably won't be able to take any plant material out with you and you definitely will not be able to bring any in. If your hiking boots aren't clean enough to meet their standards they will sterilize them for you, honest. They are not kidding about this. They have had serious problems with invasive exotic species, both plant and animal.

Paula