First up, I should say that I am a foodie - I love food, cooking, eating in, eating out, I am a member of the Slow Food Movement and I have eaten in many great (Michelin star) restaurants. Overall, I prefer food in NZ to the UK.
If you shop like you used to in the UK, your food bill will be higher here due to the decreased buying power of NZ and the seasonal variations (which Tesco et al have worked at removing). Food is season here is very cheap. Some examples I have bought:
Pears for 9c/kg
Avocados 4 for $1
Asparagus for $1 a bunch
Gold kiwi fruit 99c/kg
Broccoli 39c/head
I can go to the local farm shops here and buy more seasonal food than I can carry for $25. Also, growing anything in this climate is easy - the problem is stopping things growing
We have adapted well to the availability of foods. There are foods that we used to eat in the UK that we just won't eat here and vice versa. UK eggs are off (the are so pale and flavourless compared to the NZ equivalent) and sausages are off in NZ.
Meat here is very good except at the cheap end of the market but I find this good as it makes us eat more vegetables.
I have taken to buying out-of-date cheese from the supermarket (and even keeping it for a few more weeks) - it's half the price and has developed more taste. Excellent cheese is available from Canterbury Cheesemongers but you have to pay for it.
Pizzas and burgers we make from scratch using the excellent ingredients available. We have also started making things ourselves e.g. mayonnaise, ice cream, hummous, guacamole. Probably the only processed food we buy is baked beans.
As long as you are prepared to work with the great seasonal foods NZ offers, you will never want for a good meal here.