I leave mine chained to the bike rack while we're on holiday, but I have to admit that if I were parked in a secluded car park (like at the start of a popular tourist walkway) I'd prefer to try and have the bike somewhere a little more secure. Unfortunately even leaving it in the car itself would feel risky. New Zealand's normally pretty secure and safe, but there are always people who will try to take advantage of tourists. Have fun though - where abouts in the South Island are you thinking of going? There's some great cycling to be had, if you can get used to the prevalence of chip sealed roads!