Taking the Interisland Ferry crossing from Wellington (North Island), brings us to the first point of the South Island, Picton. It was a passby for us but you may check the place out at http://www.picton.co.nz/.
A little about the ferry
There are 2 companies that runs the ferry across both island, Interisland ( http://www.interislander.co.nz/ )and Bluebridge ( http://www.bluebridge.co.nz/ ). It is about 3 hours ride, charged by per passenger (~NZD69 per person per trip) and per car (~NZD130 for a 8-seater car per trip). Each type of car is charge differently. You may want to ask your car rental company for a package deal if you’re driving cross island.
There’s food and drinks sold on the ferry.