My girlfriend and I will be traveling through New Zealand in February. Both islands, 4 weeks.
Anyone have great tips for hiring a camper, sites, bars/music, etc.?
You'll remember that trip the rest of your life, and you'll have zero regrets outside of what you didn't get to see.
Both islands: Don't rent a camper - locals despise them and them (and their drivers) "road maggots." We rented cars and stayed in lesser cost hotels and bed & breakfasts. We bought a GPS before leaving and loaded it with purchased maps so we knew where the hell we were going.
North island: When you go tubing through the glow worm caves, use the bathroom first or your wetsuit will hold it against you...literally
South island: There's nothing better than a wild dolphin in the wild ocean swimming around you and checking you out just out of arms reach; it's worth the long pounding boat ride to find the dolphin pods, the freezing waters, and the physically exhausting funny things you have to do to get the dolphins to swim up to you...oh, and try to skip breakfast or you might be hurling it on the way there or the way back. Oh...and don't sit inside with others doing the hurling, go to the bow, watch the horizon and enjoy the dolphins leaping through the wake.
South island: If in Queenstown, take the gondola up to dinner on the mountain, take in the ridiculous view of endless glacier water, enjoy local live musicians and an international audience.
Ferry between islands: There's often a regional amateur music group traveling between islands performing for discounted tickets, but you won't hear them if you're out on deck the whole time.
Either island: stop at the roadside cafes and enjoy NZ's affordable "fast food" made from scratch.
North Island: It's worth staying at the Skotel (Ski hotel), hiking the surrounding area (you can walk behind waterfalls) and booking a guided hike through the place that they filmed as Mordor in LOR. Hiking through the real Mordor is better than any LOR tourist trap -- it's hard, it's rugged and beautiful - we almost got blown off the top and had to turn back.
South Island: absolutely do not fail get out to Milford or other fjords. By bus is easiest and you get chances to (legally) step into the rain forest (you can't carry a dead stick out of the forest) -- the most primitive and beautiful thing I've ever seen - I felt like a dinosaur to walk into view at any moment.
South Island: speaking of rain forest, you don't want to skip the glaciers -- experiencing a glacier that ends in a rain forest jungle is incredibly surreal.
That's only part of the list - it's an endless variety of activities/options. I suggest focusing on doing things that immerse you into the natural wonder of NZ that you can't experience anywhere else in the world.