Quality alcohol is probably one of the most important commodities you'd find in a post-apocalyptic barter economy. Why?
- Without large-scale water filtration systems in place, it's safer than water.
- It's difficult but not impossible to manufacture. Specialized equipment for malting, fermenting, distillation, etc. can be hard to come by. These might be even more important tools due to their function as capital to produce a valued good.
- Well packaged alcohol can last quite a while in a natural environment (use caves as cellars, etc.) So groups of people can control market supply more effectively (if there's a glut of beer, wait until it dries up to offer yours.)
- It works as a sterilizer in a pinch. Important when antibiotics aren't readily available and your autoclave is broken... :)
- At the end of the world, EVERYONE is going to want a stiff drink.
Depending on how you're looking at it, labor supply is a vital "good" in a society that needs to revert back to small scale agriculture. Basically, you'd have tribes of people who are either slaves/indentured to a local power, or have banded together as a "temp" service for communal profit - a large extended family hiring out three teenagers for the harvest season for a share of the harvest and some extra trade goods, for example.
Livestock may be even more important than labor itself, combining both a food source and a labor source in one. In all likelyhood, large-scale raising of cattle will require too much food to be practical. Instead, there would be "the family cow/horse/donkey/etc." and shepherds with flocks of goats, which are hardier and can be grazed on more unfriendly terrain. Some interesting details:
Goats can withstand heat stress and can endure prolonged water deprivation. They have additionally great adaptability to adverse climatic and geophysical conditions, where cattle and shee cannot survive. [...] Dairy goat is considered the cow of the poor. The goat eats little, occupies a small area and produces enough milk for the average unitary family, whereas maintaining a cow at home cannot be afforded by the homeowner, hence, the growing popularity of goat as the poor person’s cow.
In more northern climes, domestic sheep will be as common (or more common) than goats, especially for their wool production. Expect to eat a lot of feta cheese.
Depending on how "Mad Max" we're getting, bullets will retain their value if hunting or defense becomes necessary.
Glass tends to be too fragile to depend on when there's no police force keeping vandals and burglars from breaking windows. Plexiglass and other clear plastics become very attractive options for windows.
Honey is a good alternative for sugar that's not very "work intensive" but fulfills the public sweet tooth. Expect dried/baked honey as treats in the long term, with an established beehive being a MAJOR money maker both as a producer and a pollinator.
Salted, brined, and dried Goods like fish, meat, and certain vegetables would replace our canned goods when we run out - they last a good while and can be produced in your home with little special equipment. That being said:
Salt would become incredibly economically important again for these purposes. We currently extract salt in large factories and mines (yes, even your hoity-toity Pink Himalayan salt and Black Hawaiian salts.) When those shut down, you'd be digging by hand (unlikely) or using the age-old method of evaporating it out of the sea water. Setting up large plexiglass evaporators will help distill both salt and water - a double win. This will require a decent bit of land to accomplish at a worthwhile scale, though.
In terms of the economics, we would see broad hoarding at the start with overinflated prices vis a vis supply with large fluctuations. When the market calms down (and populations stabilize,) we'd see a return to rationality with relatively stable rates depending on production - lower for grains and farmed goods, higher for complicated, hard to replace goods like durable metal objects, quality clothes, and refined foods like candy (twinkies?).
Within about a week, most produce will have gone bad. Without the shipping infrastructure, getting fresh fruits out of season will be nearly impossible. In old still life paintings, the presence of fresh fruit, and especially oranges, was a distinct sign of wealth. There is ancient literature that describes people's wealth by stating that they had winter fruits in the summer and summer fruits in the winter. Locally produced fruits will be cheap at the point of production but very valuable as trade goods in a caravan outside of normal growing ranges and seasons. Expect more dried fruits for preservation, especially for berries, cherries, and the like. Melons don't really preserve though (and require lots of water), so serving watermelon, canteloupe, honeydew, etc. will be a strong display of wealth. Things like peanuts will be valued for their high nutrient content and long storage life (as will all legumes in general), so they will be valuable, but probably reserved for special or extreme occasions (either a celebration or a food shortage) which will keep their price in check - people won't consume them as quickly as other, more perishable produce.
In the long run, we'd probably start substituting a more readily available good for the latter category - like the aforementioned honey for candy, wooden items for metal, rough woven cloth for manufactured cotton, etc. Eventually, it will be so commonplace that using a metal spoon will seem strange to the average individual. Only "collectors" will be interested in these special items, and will probably be willing to pay a premium for people able to find "vintage" relics of the "earth that was."
PS: dried grains wouldn't get "used up" - you always preserve enough of your harvest for AT LEAST one year of sowing, preferably two (in case one crop fails.)
Week 1: panic. massive looting, little real economic activity. Formation of raiding/looting groups.
Week 2: most unprocessed food starts to spoil. Panic driven trading and inflation. Groups will start to merge/compete/disband/fight. Some will probably start to engage in long term planning, such as creating mutual defense pacts and farming/trading collectives.
Month 2: people start to settle down from panic and focus on short term survival. Durable goods, seeds dominate trading.
Months 3-6: depending on the season, people focus on purchasing livestock for animal labor and interim food supplies while crops grow. Travelling labor collectives and small towns form.
Month 12: People coming to grips with a year of post apocalyptic living. Longer term planning starts to come into effect. People focus on making tools. Metalworking repair skills will become very valuable to keep equiment functioning. New metal will be harder to come by. People began to craft rough metal and wooden tools as replacements. Medical supplies become scarce, people start dying from basic bacterial infections. People start substituting beer for suspect water. Evaporators set up to provide for fresh water and tradeable salt.
Years 2-3: Expect to see the first batches of distilled alcohol, low percentages, not well aged. Also expect to see methanol poisoning. Possible establishment of some sort of currency - either grain, peanuts, or workable metals.
Years 4-10: Food prices stabilize locally based upon available producers and inter-regional trade. Non-seasonal fruit recognized as a status symbol. Very few pre-apocalyptic durable consumables remain. People shift consumption to renewable goods. Assuming that they aren't burnt for warmth, books are valuable sources of knowledge and entertainment. Many modern books will decay due to exposure (your paperback is made of VERY cheap paper).
Second decade: Children of the apocalypse come of age. Raised without cultural trappings, they will find plasticware and metal utensils strange. Wealthy older people become collectors willing to pay money for rare items.
Third decade: The start of larger governments, either warlords or something resembling the Senate of old. Stability means people start to recreate old knowledge of medicine, science, and technology, trying to preserve what they remember before it becomes irretrievably lost once the next generation takes over.