If everyone stockpiles individually for themselves and their families then you have a massive distributed cache that is more resilient that a centralized warehouse that can be bombed.
You seem to think the responsibilities of "the state", "the military" and "individuals" are distinct. They're not. Some individuals like to pretend they are, and rely on the government to do X (and some governments play the same game and rely on individuals to do Y) but reality will always eventually assert itself, whatever system of government you prefer.
But they won't stockpile individually, because it's in no one's individual interest to stockpile. (This is an example of the Prisoner's Dilemma).
I agree with you that "reality will always assert itself" but I'm having a hard time understanding how anyone things that Libertarianism can be that reality.
Libertarians act in the interest of preserving freedom in the long term, not maximizing personal wealth in the short term. That's one of the key differences between Libertarians and Anarcho-Capitalists. A Libertarian might stand up and say, look, our neighbours our hostile, I really think we ought to stockpile food, and if people are convinced (because it's true) then they'll do it. But the government will not say "we need to stockpile food so we're introducing a stockpile tax". Do you see the difference?
I completely agree that Libertarianism can't be retro-fitted onto any existing human society.
I do see the difference, I just happen to fancy my chances better under the system where the government imposes a stockpile tax than the system which leaves it up to the market -- even more so when, as I've mentioned in other posts, it's not about stockpiling, but about maintaining self-sufficiency in the face of an alternative that is more "efficient" economically.
Regarding your second paragraph, and completely independently, how do you propose we reach a libertarian society from the position we are now?
And how do Libertarians ensure that those they share a state with act "in the interest of preserving freedom in the long term, not maximizing personal wealth in the short term" in the particular cases where that may be non-rational?
They can't. That's the flaw. You basically have to start again with a bunch of Libertarians who raise their kids Libertarian (this is the easy bit) without it descending into a cult (this is the hard part).
The problem with retrofitting it is unless you already have the no-coercion culture and infrastructure in place, too many people acting in their personal short-term self-interest find coercion easier. Which doesn't mean mugging people in the street; it's as mild as "my vote for your handouts of their money".
Well it depends on other factors, but that's not the point. In this situation:
* Firstly, who's to tell Liblanders that they risk invasion? It's not clear that Libertarianism supports the notion of foreign policy, diplomacy, espionage etc.
* Secondly, all the food in the country is coming from Xia. Once demand grows Xia realises that Libland has recognised the threat and invades immediately.
The same way we find out about anything. Companies like Reuters and CNN tell us while the CIA is still snoozing.
It is entirely clear that Libertarianism does support those things and one of the two roles of a Libertarian government is the physical security of the nation and its citizens.
OK, I'll grant you the existence of the media reporting from foreign countries (although I fail to see how the "What's Xia up to" branch of Reuters makes any money).
Now, a worthy chap sees a report about Xia on CNN and gets suspicious. How's he going to get enough money to mount a publicity campaign warning Libland citizens of the danger?
There might be food insurance companies. They would have advertisements telling people of a probable military intervention by Xia
and recommend people to buy food insurance in order to be safe.
Regarding your second point: The realization that Xia might attack will probably not come suddenly but slowly. So people will
gradually begin investing in food insurance. It's unlikely that Xia turns from friend to enemy in a matter of days.
The realization that Xia might attack will probably not come suddenly but slowly
Just like 9-11, Dec 7, 1941, the anschluss, mongol invasions...the Hitties and Philistines versus the Israelites, yeah, military ops are always telegraphed.
"Austria was merged into Nazi Germany on 12 March 1938. There had been several years of pressure from Germany and there were many supporters within Austria for the "Heim ins Reich"-movement, both Nazis and non-Nazis." - http://en.wikipedia.org/wiki/Anschluss
Your less specific in the details of your other facts so it's hard to get specific counter-facts on them.
You seem to think the responsibilities of "the state", "the military" and "individuals" are distinct. They're not. Some individuals like to pretend they are, and rely on the government to do X (and some governments play the same game and rely on individuals to do Y) but reality will always eventually assert itself, whatever system of government you prefer.