Mrs. M and I doing four weeks next March in South Island. Start at Queenstown, do the four day Milford Trail, then down to Stewart Island, up to the Banks Peninsula, pick up a car from Christchurch and head north for a circular trip to the north and back down the west side and probably Arthur's Pass back to Christchurch. That loop will be about 12 days. Mrs. M. into wildlife particularly birds, she likes hikes (and likes me to hike) and we both enjoy our wine. (Edit to clarify, we fly into Christchurch, Banks Peninsula for a couple of days then the 12 day drive starts with us heading north up the east coast).

Are there any "must" things we shouldn't miss from Christchurch onwards?

(We have a spare day or two in Queenstown and Christchurch, but don't intend to loiter in Invercargill - fly in and out).