apparently you've never been to the central plains in New Mexico around here everybody lives on food stamp and horse-trade is the model so maybe not in prehistoric times but in modern times yes... barter is a way of life... By the way the Egyptian store grain and wheat was actually the first commodity that was used.
The measure was the amount of wheet that you could scoop out in 4 handfuls (put your hands together side by side Palms up scoop out 4 handfuls).
if you try this as an experiment you'll find out that what you get is roughly a pint of wheat ( if you put it in a pint jar) and its total weight is roughly one ounce.
. And that's relatively close to the weight of a shekel
later on the Sheckel became the weight of standard.
however when you consider it using grain is not barter grain is a currency because you eat the Grain and you have to eat it before it spoils because wheat is known to collect a certain mildew that will kill you if you eat it. therefore you constantly need it to survive no matter who you are and everyone grew it out of necessity and because there was enough land to do so.
there for , somebody has a surplus and somebody doesn't have enough. So the one that has a surplus would hold the one that does not have enough in debt as a debtor until the following growing season when he would have to repay what he was giving up front the previous fall or work it off..
and if you had wheat then it was accepted as tender for any other goods or services you may need
Especially toward late fall