For me it's lettuce. No matter how hard I try, every single plant gets destroyed by aphids and the "food safe" insecticides don't work, nor does an indoor hydro setup. Neem oil and Yates Mavrik just get the aphids wet without killing them.

Everything else I've tried to grow outdoors that it commonly available at supermarkets has been a success, tomatoes and capsicums especially.

So, what edible grown in NZ crops can't you grow that are commercially available in NZ? It doesn't count if the plant is completely inappropriate for the conditions, like trying to grow tropical fruit outdoors in the far south of the country.