Onward Travel

I am thinking of going to Fiji and have NO idea when I will go. I know I need onward travel. What is the cheapest ticket to get? Maybe, a boat ferry to Tonga or somewhere? I just have no idea when I will be ready to leave.

There is no such thing as a boat or ferry to Tonga, or any other Pacific country, which you can book. You will have to have a flight booked. You can choose from Air Pacific (which may be prepared to refund if you cancel before the flight, or change your booking date - check terms and conditions before you book) or Pacific Blue (Virgin), which has lots of conditions, especially on their cheap fares.
Other Pacific countries do have flights out of Fiji on national airlines, so you may need to check these to. There is a list of airlines servicing the Pacific Islands in the FAQs at the top of this branch.

Air New Zealand used to refund the unused portion of a ticket. I don't know if they still do this as lots of travellers would buy a return ANZ ticket then get a refund for the unused return portion, so maybe they wised up and stopped doing so. But it's worth checking out.

What about this? At the bottom

http://www.timelesstuvalu.com/tuvalu/export/sites/TTO/DiscoverTuvalu/gettinghere.html

Good luck with the boat schedules! Don't expect them to be anything like reliable. They do have an email address, though, so you oculd enquire.
Meanwhile, how do you then get out of Tuvalu, except back to Fiji?

I think if you fly Air Pacific you can book a round-trip ticket to one of their destinations, say Vanuatu but there is a mandatory stopover in Nadi. When I was looking at tickets it appeared that you could choose how long this stopover was, so if you want to travel round-trip and go to two countries you could do a 1 week stopover in Fiji then continue on your way to your final destination for the price of one round-trip ticket. There did not appear to be a mandatory stopover on the way back. My understanding is that Nadi is the main hub for Air Pacific flights.