Of course I know Hawaii is a state but it is not connected to the mainland and that makes getting supplies there almost nonexistent if the mainland states are fighting and no ships going there.
You said, “But fuel and power are not needed for heating there. And days are long.”
You are very nearsighted when speaking of fuel and power not being needed for heating - as though fuel and power isn’t needed for anything else. Fuel cooks food, fuel runs cars, fuel makes light, fuel is used every minute of the day and it comes by SHIP. Electricity is very expensive and I said very few houses have cooling due to the expense.
I know from being there and finding out, fuel comes by ship - if no ships, no fuel except driftwood or whatever. None of those islands can do without fuel from ships unless the populace catches fish and eats it raw or makes a fire and I hope they would still have matches left over from a ship bringing them there or they have a fire maker bar that another ship brought. Maybe they have a cigarette lighter left over from a ship bringing that - they wouldn’t have to use it to light a cigarette since there wouldn’t be any cigarettes since they come by ship. Maybe they are good at rubbing two sticks together. They have little building material, not much wood, because that comes by ship to build buildings.
At least you say “a fraction of the population would die before self-sufficiency got underway...” Here in these connected states it will be much easier to find what is needed to repair and rebuild and have power.
You head out to Hawaii, build a grass hut and fish, (take matches or a flint bar) and I’ll stay in Texas.
Ships have been known to come from other places than the US. Hawaii could simply buy its fuel on the open world market. Who is going to blockade them?
I am in Washington State (eastern part of the state — arid — more like western Texas) and am familiar with both Alaska and Hawaii. I don't think you have spent much time hanging around banana farms or coffee or sugar cane plantations (of course, many other tropical or sub-tropical crops can be grown). Not much of a problem starting a fire -- have you seen the lava dripping into the sea recently? Seriously, Hawaiian military bases have plenty of methods to make fire! On the outer islands of Hawaii and distant reaches of Alaska cars are not that important — no or few roads in peripheral Alaska and no compelling reason to take a touristy drive around the island in Hawaii during a civil war! Not sure why local transportation is a big issue, or the other comforts of current day life. The scenario is addressing a time when few or no of those luxuries will be available in any state.