Supplying 3 months of bank statements is a general requirement when applying for a loan, so this will be part of the paperwork we ask you to supply. Not so that we can browse through all your food purchases, but to make sure everything's in order.
It's pretty simple, but in case you get stuck here are some step-by-step instructions for the main banks and IRD:
If you need to provide proof of your income, you can do that through Inland Revenue.
If you don't have mIR you can contact IRD to request a summary of income on 0800 775 247.