I've been to Aucland last time and I'm planning to go to South island next March-April.
What are must-do things and must-go places?

Kia Ora Tomoko! Hi.
I was born in the South Island so it has a BIG place in my heart.
Nelson is an absolute must must got to, Abel Tasman National Park is very close to my bliss, most beutiful beaches you have seen anywhere in the world! Wine region is Marlborough, West Coast gold panning! Enjoy

Thanks for your tip. i definetely go to Marlborough. hahaha

Queenstown is a wonderful place, lake Tekapo cannot be missed either ... I spent two weeks in South Island a few years back, renting a nice SUV and drove more than 2000 kilometers!

the routebrun trek is great and queenstown is the adrenalin capital - try and also make time for abel tasman national park which is stunning

Thanks for your tips, Bobby and Wayn.

the catlins is a nice spot also

The south Island is probibly the most picturesque of the two islands and it depends on what you want to see. For golden beaches, rainforests, vineyards and sunshine, Nelson and Tasman are the best (at the top of the South Island. Until two years ago I would have said for the most historic and picturesque city, visit Christchurch, Since the earthquake the central city is pretty much closed off and many of the wonderful buildings have gone but it is still a great place to visit and use as a base for seeing skifields, Kaikoura (Approx 2h north), Akaroa (approx1.5hr southeast)and Hanmer hot pools (approx 1.5hr northwest). Queenstown is set on a picturesque lake, surrounded by mountains and skifields with plenty of extreme adventure activities. Dunedin is a city that harks back to its scottish root. It also has the world's steepest street, a royal albatross colony, a penguin colony and a castle you can go through. The West coast is the best place to see native forests and the only place

In christchurch have a cpa
a cuppa @ park royale

Do the milford cruise..visit fjordland, te- Anau caves n boat trip..in queenstown..go jet boating on the shot over river..totally awsome..g white water rafting, helicopter ride is awsome as well..ASK the PIOLET TO DO SOME NOSE DIVES..they r verry good at this sort a thing! ..tjere is so so much depends how much time U have.. T. Hut..mt. Cook..Hast pass, buy some awsome Jade in greymouth area? I also enjoyed the frank josef Glacier walk..whale watch in Kaikoura..chirch of good shephard has awsome views/vistas...i hope i can visit soon..