That is money in some societies. Money is simply the most marketable (widely accepted) commodity. There have been many societies where a measure of grain was money.
Money often in the past was silver or gold because they were the most widely marketable commodities and would be accepted for trade across wide areas.
money is a coin or paper representation of goods or services, once it becomes food it is just barter or sharing
and if I have too much grain don't share it to people who need to eat then I am just a demon
there are still some sane communities that just all work to make food and share it all, along with making clothes and shelter for each other