SEF, I will try to clarify your concerns and questions,
1, here in NZ, we already have suppliers of Outdoor gear and Firearms. Good selection. High prices.
Pacific Islands- Importing any weapon (including a Speargun or Flare Pistol) could land you in a Rat and cockroach infested cell for a long time. During this time, You would be relying on Friends and Family to supply you with Food and other necessities. No Family? Starve..
I'm not exaggerating, it happened to a friend of mine in Tonga a couple of years ago. He escaped.
Local laws and lack of disposable income would severally restrict any Retailers from making a living.
Knives in the Pacific are very basic and CHEAP. The only People that carry expensive high Tech. Ones are tourists passing through that haven't had them confiscated as Weapons.
With the exception of Customs and Police Officers of course. (same everywhere in the World)
2, Survival by Slingshot launched Arrow? You would lose a lot of weight quickly..
Good fun trying to shoot fish with a bow, (personal experience) but more successful off a boat with Spear gun.
On shore, a multi prong spear is definitely more successful and is what the Locals use.
Long term, fishing with Nets is the best way to thrive. Local Laws may restrict this practice due to its success...
Most Locals are restricted ($) to fishing with hand lines for small (<6 inches) fish which take a lot of time and effort.
3, Nano Tech. Would be successful IF, you had a power source and I guess access to the Internet.
i.e. probably not in a power down E.O.W situation.
In Rural, isolated areas, Bartering is the way to go and has been since the start of time.
Cash is not always available to locals as it is often a Agrarian economy, not cash economy in lots of places World wide where not highly populated.
When up in the Islands, trading is the accepted (and preferred) method of procuring goods and food for non locals living in area.
Locals will try to get Cash from Tourists passing through. Locals just do not have Cash incomes in most cases. Not something we are used to in the Western World.
4, Sharks ? Consider yourself lucky if you even see one.
According to figures I've seen, (see Movie Shark Waters) 94% of Sharks have been wiped out since 1900.
Seems about right.
Bare in mind, they are Predators, and don't make a living by advertising their presence...
SEF, you are obviously keen on being in Survival mode, why don't you come down and give it a go?
You'll never know till you try...