I last flew NZ from LAX-AKL back in 2014 and it was in Economy. After the meal service was done and lights switched off, most people had gone to sleep but I was still awake watching movies. The flight attendant actually came over asking if I wanted any drinks or if I was still hungry and he even offered me another dessert which obviously came off another meal tray. I think it's more NZ policy that they don't keep the food and I fully understand that for food safety reasons.

That being said It's certainly possible... Earlier this year I flew ICN-BNE on Korean Airlines (in Economy) and I fell asleep before the meals were collected but I also hadn't fully finished the meal. When I woke up they were just about to serve breakfast and one of the flight attendants came up and said that they'd kept my dinner from last night if I wanted to finish it but they could also give me breakfast as well. Needless to say, I didn't want any more of my dinner from last night but I was extremely impressed that in a cabin of 250 seats they were able to keep individual meals.