There is no ATM aboard QE2, so I suggest you bring travelers checks which you can cash on board. QE2 is a no-cash ship so you won't need money on board, and you can also use the ATMs ashore.
I had expected an ATM and traveled as usual with little cash. It was almost a disaster! Take along a credit card for shipboard expenses and more than enough travelers checks. The ship won't accept personal checks or give cash advances on Visa.
If you can be 100% sure that your card will work at an ATM ashore - use that.
We find that often we arrive at a new port/country and get ashore before the banks are open. We then beeline for the 1st ATM we see and draw out the cash there.
It saves having to cash up travellers cheques.
At the end of the voyage we hand over our unused foreign currency as tips (provided that it's a reasonable amount of notes).