What kind of trip are you planning? Are you going to stay in a specific area or tour around the island?
I spent 10 days in a camper van touring around the south island a few years ago. I started in Christchurch, then went south towards lake Tekapo, then Queenstown, Milford Sound, Wanaka, the west coast and crossed back towards Christchurch.
The scenery was amazing and some of the places are just so enormous and distant a telephoto lens makes perfect sense for landscape photography. I'm thinking of around lake Tekapo and Pukaki in particular. I went up Mount John Observatory and was welcomed with a breath-taking panorama of lake Tekapo on one side, and a vast vista of... nothingness on the other, backed by snow-capped mountains.
I used my standard 17-50mm zoom lens almost all the time, and my 100mm when I needed something longer (crop body). I didn't feel the need for anything wider, however I wished I had a longer telephoto lens. I'm saying that as someone who usually prefer to shoot wide over long, but NZ landscapes are so big, there'd be too much of nothing in the frame if I were to shoot ultra wide.
If you can, bring the telephoto lens with you.