Stay safe! Literally - the region is quite isolated so if you get in trouble you may have difficult getting medical treatment or emergency assistance in a hurry. Ensure your spare tyre is in good condition, your emergency kit is stocked up, you have a full tank of fuel, some emergency food and drink, warm clothes and a map; because it could be a long wait if you have a mishap or a long walk to the nearest place to get help. Also, be prepared to stop and assist another traveller in trouble.
contact
Do not rely on mobile telephones working outside of urban areas. This part of the South Island is part of the 5% of New Zealand that cellphones don't/won't work because there is no network coverage and insufficient demand to justify any. And if there is coverage it is probably only available from a network provider that you do not have a phone for.
It is possible to use SAT Phones and some businesses may give a SAT Phone number as an alternative contact number.
Internet access can be found in the libraries of Westport and Greymouth. Some Holiday Parks may also have Internet for a fee.