Mapua (just outside of Motueka) - fabulous fish and chips - get them and take them over to the wine bar to enjoy with a lovely glass of wine, or get a glass of wine and eat them looking out over the sea.
Abel Tasman is amazing - beautiful walks and also well worth catching the ferry round to Fairy Cove and walking back. Or go kayaking!
If you love wine, then Marlborough is where it's at for white wine, particularly Sauvignon Blanc - don't miss the Cloudy Bay winery, or Peter Yealands. If you love red, then Otago - try the Roaring Meg winery.
Have to say, unfortunately places in Christchurch tend to close rather early of an evening - so keep that in mind. The Quake Museum is good, there's increasingly good shopping in the CBD, and there are some very nice restaurants - for fusion, we love King of Snake (if that's still going), if you love a good steak, then Bloody Mary's is fantastic, and for Greek, we highly recommend Costas Taverna. The Botanic gardens are nice for a wander, there's punting on the Avon. A good beach in Christchurch is Sumner - and you can have a bit of a squiz at some of the damage wrought to both the natural and man made environs of Christchurch there, too.
LOL at your friend getting stuck in Murchison for three days slug. I used to live there, so I feel their pain! The roads are fairly busy at that time of year, particularly with the Kaikoura road still limited to daytime traffic.
Going the Kaikoura route - it's wonderful to see the seals, whale watching is great, and make sure you get a good feed of Crayfish (Nins Bin). Once again, you get to see what the earthquakes have done. Be prepared for long stops for roadworks though, as they repair the road while trying to keep traffic moving.
Please remember that while we Kiwis generally pride ourselves on our friendliness and hospitality, there are two legged arseholes all the world round, and make sure you do everything you can to keep yourself and your belongings safe. Travel Insurance is a must.
If you do go hiking, make sure you take sensible precautions like leaving where you're going and when you expect to be back details with someone, take plenty of warm clothing, food and water etc.
Enjoy! (Oh, and yes, New Zealand is not a cheap place, prices will seem expensive.
(Sorry for the novel, I'm rather homesick today. . .)