This is a great idea, Kiwi Flyer! I tend to agree about the vehicle thefts. A couple years ago I was traveling in Northland with my two daughters and we parked along the waterfront in Paihia to have a picnic at one of the tables that lines the roadway North of downtown... We watched a couple of kids who couldn't have been over 14 years of age casing the cars in a parking lot nearby. They opened what appeared to be an unlocked door and made off with a large paper bag that was on the seat of a car. I telephoned the local gendarmes and reported the crime, giving a description of the two suspects. The police officer indicated that the kids he suspected were well known to them.

The OP can try contacting this place to ask if they can store his bag for a day... http://www.bayadventurer.co.nz