Sugar, Salt, Rice, Beans and canned/dried meat will all keep a VERY long time and are VERY cheap in the current economy.
So are several spices, anything from common pepper to chili powder will be VERY necessary to make otherwise bland/spoiled food palatable.
Remember, there have been wars fought over Salt, Pepper, Nutmeg, ect. and there is no reason to think that they won't be in great demand in the future.
Things like baking powder, baking soda, yeast will be in demand.
Yeast cultures can be kept alive indefinitely with a little water and something for them to feed on...
Anyone familiar with sour dough cultures transported in crocks in the old days or fermenting yeast cultures used for everything from cheese to brewing beer/distilling spirits?
Renewable produce like tobacco, Aloe, ginger and any other medicinal plants will be a very good thing to have.
Dill, peppers, and produce to make vinegar/wine like apples, grapes, strawberries will be a 'Currency' commodity.
People WILL have to preserve food, and the basics for that process grow wild in some places,
But for most of us, having them cultured in the back yard will be a HUGE benefit that is immediately available.
Don't store 'Ammo' unless it's for yourself and you KNOW the caliber is 'Usable'...
Stockpiling .22 LR ammo for small game will ALWAYS be a very good bet!
Everyone I know has a .22 rifle or pistol, so that ammo will NEVER go to waste,
And it really is the only 'Universal' ammo that would certainly be used up or traded.
If you are going to 'Stockpile', then concentrate on popular calibers RELOADING.
If you stock .30 caliber bullets, powder, primers, then all you have to do is change dies, which ARE NOT perishables.
I see used dies in strange calibers every gun show or swap meet, and if I can get them cheap enough,
I put them back for later use.
Common calibers would be anything from .30-30 to .300 Belted Magnums and everything in between.
They all use common primers (Large Rifle) and common bullets (.30 Cal.) and for the most part, common powders so you can RELOAD pretty much anything in .30 cal. that walks through the door and vastly expands your capabilities and usefulness to the community...
Useful people are protected.
If you choose to stockpile .22 Caliber supplies, do the same thing,
.222, .223, .220 Swift, .22-250, .25-06 dies, ect. will make what you stockpile more usable.
Midway USA is advertising a progressive press for pistol and up to .223 calibers for $150 right now,
And that's a pretty cheap production scale way to do things if you intend on doing something like this.
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Something as simple as a clean, deep water well is a barter commodity.
Canning jars, but especially lids, paraffin for canning jars will be a very long lived in storage,
And if you can food or anything else, it will be invaluable.
Like I said before, stuff like welder and welding supplies if you can afford to store them will be a GREAT thing to have,
If you work in a paper plant or warehouse, then stockpile the 'Factory Seconds' you run across cheaply at work,
If you work in the medical profession, then stockpile the stuff you see thrown out every day, something as simple as tweezers or sutures or hemostats will come in VERY handy to have.
In a world where the electrical grid breaks down, the guy that carted home a bunch of electrical components will have some very serious barter material...
Someone will need to keep all those 'Improvised' generators working!
The guy that works in an auto supply house or parts store might have those bearings or brake pads you need for a vehicle or project...
The 'Junk Man' might be able to sand cast parts or cast brass parts not available anymore, and that would be a VERY good skill to have.
Raw material of any kind is always money in the bank when someone needs it.
No single person is going to be able to stock pile EVERYTHING they will need,
But a network of stock pilers will QUICKLY develop a trading community for goods and services,
And if you have 'Skills', then you will be on the fast track to getting what you need and making 'Friends' along the way...