The back row in economy where there's only two seats are my favourite seats in economy on air nz. I think I've been lucky in that I never seem to end up with anyone in the seat next to me so I get a spare seat next to me giving me space and privacy if you want to do work. I sit next to the window so never experienced any cart issues.

I also have a theory that they're less likely to fully fill rows of 3 right down the back but never tested this with 2 people. I go for the row of two. There's also usually been the row of 4 in the middle at the back that's been free. You'll have time to eyeball the cabin from the back and see if there's other free seats around you might like to switch to after the door has closed.

Sometimes despite the big planes economy is very full.

My preference is the back of the plane rather than further up the front. It is preferred seating so I buy the seat + bag option rather than the works (comes with meal but is 20-25 extra) and spend that money on the preferred seating and just eat prior to the flight. It's a short flight really so easy enough to eat before or after flight.

The alternative is to book a row of 3 down the back (just standard seats) and fingers crossed the planes not super full and your partner could scoot over one if no one sits next to you by the time doors close. You'll be testing my theory for me