Oh, and for gold:
I think it has its most use in converting wealth to whatever new currency is implemented. You might lose wealth in the transition, you might lose more in a currency transition. Or if the current currency remains in circulation but is printed to the point of extreme devaluation.
Trading real gold for groceries seems like a bad proposition.
But being able to go into a bank and trade gold for currency seems like a winner.
If we're talking mad max world, I don't think gold will have that much value in the short term, either, except for maybe when civilization begins to emerge again. I also don’t thnk that would take very long, 5 years tops, unless some sort of major die off happens (like a super bug/plague). Of course, if you survive some sort of mass die off, what did you lose by storing some gold? You're not going to store thousands of dollars worth of food in its place. Ammo will store indefinitely, as will most of the components used in creating more ammo. Ammo for trade in an end of the world mad max scenario makes sense. But, you can only store so much ammo, too. Several ammo cans of each common caliber, or each caliber you own, will begin to take up alot of space. And, in trade, its only of use to someone who has a gun to begin with. There is enough ammunition stockpiled around the country that stores might take awhile to begin to dwindle. Of course, giving someone ammo who doesn't have it already means they just might decide to use it against you in a bid to take everything you have.
Of course, as a means of self sustenance, hunting is problematic at best. Firstly, as the hordes go forth from the city to the wilderness, animal stocks will be depleted rapidly. After a year or two, when all major stores of food are dried up and people begin starving to death, the animal populations might begin to return. Some species may be regionally hunted to extinction, though. If I were planning for mad max, I'd invest in some animal traps and learn to use them.
