Do be careful on your drive to and from Punakaiki. Despite the best efforts of man, nature is an odd duck that likes to constantly wear away at the cliffs through the use of waterboarding. In this particular case, The Tasman Sea was doing a little work on Highway 6!
You never know when a coastal highway will give way like this, so make sure you drive safe and keep alert on these roads! I have included a link to the national transit board for New Zealand which provides up to date traffic conditions.
On the way out to Punakaiki, there will be a few small towns, however they are very spaced out. On this particular trip, my wife was nice enough to let me stop for a restroom break on the side of the road... and now I know it was because she wanted to take a picture!
As a general warning, make sure you take advantage of the rest stops you have along the way, otherwise you will be forced to use a different disposal technique much like I did.
The West coast of the South Island is, hmmm, how can I put this? Damp - VERY damp. It does have a rainforest climate after all. I have never known such torrrential rain - go on and on and on and on and on and on and on.
Compensation from that 'soaking wet through' feeling occurs when the rains stop, the clouds lift, and a breathtaking shiny green landscape is revealed before your very eyes.