The cartoon series La Brousse en Folie and Le Sentier Des Hommes by Bernard Berger will give you an insight in the local culture and tradition. The comics are written in French, the former imitating the local accent and grammar or lack thereof
Other than that, plenty of conventional souvenirs shops may be found throughout Noumea.
costs
New Caledonia is very expensive, since much of the food needs to be imported. There is no culture of bargaining either and attempting such might cause offense.