Fremmer said:
Value is determined by what somebody will pay or trade for the [whatever].
That's a good definition of price, but not of value. Value has nothing to do with money and nothing to do with what anyone else thinks an item is worth. Value is simply the reason one decides to possess an item.
In other words, an item has value to someone simply because for that person it fills a perceived need. Value comparison is nothing more than deciding whether Item A has a higher usefulness to resource "tie-up or depletion ratio" than item B.
This relates to ammo very directly. Having plenty can be either savings or insurance, and it can be both at the same time. Savings, in that it could be bartered or converted into cash. Insurance, in that it's a hedge against an unknowable possible future occurrence.
For most people, there is value in holding ammo as savings and/or as insurance, but there are limits. One's ammo supply is valuable only to the point where he perceives that its usefulness as savings and/or insurance is outweighed by the amount of resources it ties up, precluding those resources from being used for something else. Economists call this "opportunity cost."
Ammo as savings:
If Joe has 100,000 rounds of 5.56 and a AR-15 with lots of mags, but no food and no place to hunt, his ammo has savings value in that it can be converted to cash which can in turn buy food. It has little value to him except as convertible savings; he is compelled to convert that savings into cash or barter it for food so he can eat.
He could use the gun and ammo to steal food, but let's assume he chooses not to go that way. Besides, at that point the ammo ceases to be savings and becomes a form of insurance.
Ammo as insurance:
Assume Joe has 100,000 rounds of 5.56 and a AR-15 with lots of mags, and he has enough cash to buy food. If the enemy invasion comes (could be a uniformed foreign army, or zombies, or...well, you can fill in this part), Joe is insured against being unable to contribute to the repulsion of said invasion, both in personal and collective terms. Or, if the invasion doesn't come but the civilized world goes to seed anyway, he can conceivably use the gun and ammo to compel someone else to feed him.
So, whether the ammo is savings or insurance depends on Joe's circumstances. Which is more likely? Each of us can decide as we choose.