As a country, New Zealand is very protective of its environment, which is demonstrated by the vigilance of its border controls. Although they are very fussy, customs officers will greet you with a smile and their good humour will make this stage of the trip bearable at least.
For a stay in New Zealand of less than three months, there is no need for a tourist visa. You only need to provide a passport that is valid for more than six months. You may also be asked to demonstrate that you have sufficient funds to cover your needs during your stay, so plan to provide a bank statement to ensure that you can leave without any issues.
As there are no direct flights from France to New Zealand, I suggest that you check out the visa situation in relation to your stopovers as well. Some people have missed out on their trips for this reason!
New Zealanders are very switched on when it comes to protecting the environment and you will see this when you arrive at border control. In fact, it is not possible to introduce the smallest amount of dirt from another country. If you are traveling to go camping and are carrying all your equipment, it is better for your kit to be brand new (or at least extremely clean). Otherwise, you risk being made to wait and pay for your stuff to be cleaned. As far as walking shoes or boots are concerned, I suggest that you wear them through customs on your feet unless they are brand new. This will save you from having to wait while they are cleaned: at worst they'll ask you to walk over a disinfecting mat.
New Zealand border control will be unyielding when it comes to certain products - and the fines can be very high indeed!
In fact, the customs officers will take a great interest in whether or not there is any cheese in your bags. It is entirely prohibited to bring any cheese into the country, and if you decide to test this out and are caught, you'll be facing a lot of expense! Similarly, all fresh produce is prohibited.
Finally, don't attempt to introduce any seeds or other plants into New Zealand, nor any animals - this is totally illegal. In fact, the Kiwis protect their territory to ensure the balance of their natural ecosystems; this could be affected by the introduction of new species.