I wonder if the Big Island could technically be food self-sufficient?

Not with its current population.  

One question that doen't seem to get addressed is the gross over consumption of food by the developed economies. Hence we assume that the amount of food demanded is the amount needed. It is well documented that the health of the UK population improved during the rationing in WW2. I am not suggesting anything as drastic but there is certainly room for redistribution and rationalisation in the current food chain. Shock horror - Big Macs Must Go ;-)
While the health of the UK population increased during the rationing period, that had more to do with a more equitable distribution of resources than with less food being consumed.  Pre-WWII many many of Britian's poor were unable to aquire reasonable amounts of healthy food.  Rationing was combined with the introduction of free school lunches for poor children, OJ rations for all young children, and milk and eggs for pregnant mothers.  I think that was what really impacted Britian's health.
I don't go out to eat often, but when I do I notice one thing.  At the Buffets, people waste a lot of food.

I cook as a hobby, and I grow food as a hobby, and I study food plants as a hobby.  It shocks me that even those that come from low food regions in a few years of the Plenty of the US, adopt the same food habits of the Rest of the Citizens, or more accurately the wasteful folks.

 We as Americans waste a lot of Food.  We have laws in some cities that state that once its cooked and not eaten by the customer, we have to throw it out.  We have "Grand Buffets" where the left over food could feed some families for WEEKS!!  It all goes to waste!

So yeah, as the end of our "Easy Eating" Lifestyle comes to and end we will see the end of the Buffets, or at least the end of them as we now know them to be.

Hey I am moving to a small town,, How many buffets are there, I bet not a single one.  Gee I wonder why??

It isn't just buffets. Fast food restaurants throw away enormous amounts of unsold food. They usually keep enough food sitting there to fill your order immediately (unless you order something unexpected) so they can call it fast food.  Whatever isn't bought in a fairly brief period, gets tossed.
I used to volunteer at a soup kitchen, and they received  boxes and boxes of donuts that weren't quite fresh enough to meet Dunkin's standards. I wonder how many donuts Dunkin and KK toss every day
I disagree.   Some numbers to consider (from http://co.hawaii.hi.us/bigislandag/default.htm):

  •   500 acres produces  7 million pounds of guava
  • 2,700 acres produces 36 million pounds of papaya
  • less than 400 acres produces over 1 million pounds of taro, a traditional food of Pacific Islanders

This all sounds very productive to me. With over 60,000 acres of agricultural land being recently released from sugar cane production, farming just this land would require supporting about 3 people per acre to be self-sufficient on the Big Island.  Statements from John Jeavons indicate that biointensive farming would support over 10 people per acre sustainably.
One of they ke advantages of Hawaii is the temperate climate.  They only use about half of the energy per capita that is used in Texas.