The devil’s in the details in world-building. This mythical figure also dips into power bases and currency so your story’s world should reflect that. By power bases, I mean those corporations, governments, or individuals that control enough aspects of a world that they could crush the little guy. Imagine Amazon.com as the Evil One killing the little mom-and-pop places. In our modern society, the power bases tend to focus on those giants who controls the power grid, the information access, and the flow of resources. If you doubt this, think about who controls the oil, which computer giant is practically on every computer, and what happens when clean water is in short supply.
Contemporary settings are easy in that regard. Everyone knows that modern society uses coins and bills. The writer simply matches the right currency to the correct time and place. Fantasy and science fiction differ though. The writers of these genres can stretch the imagination. The money could be significantly different and the power base behind it may not be as obvious.
Fantasy settings can feature a barter system, coin economy, or use of weighed metal nuggets. However, the writer must still think about what item or core idea is of supreme value in this system. Most folks grow their own food so that’s probably not the power base. Is it safety since the town depends on the Lord/King’s troops against the marauders? Is it land ownership?
Coins are easy but are they the standard value of gold-silver-copper? In a metal poor society, the coins might be wooden or clay. How many silver bits go into a gold piece? Even if your character doesn’t need to know the exchange rate, you do. This way, when the character goes shopping for something, they would know whether three gold pieces for a new bow is price gouging or reasonable.
Whose face or emblem is on the coin? Are the same coins accepted across all kingdoms/towns? The important answers show the reader where the power base is, which is probably with the one who controls the government, and therefore the citizens’ safety. If the merchants accept the same coins across kingdoms, then that implies treaties and mutual understandings are in place. For instance, the Lord of the Rings movies did not pay attention to currency for paying for anything, like drinks in a tavern. However, this implied that all the various kingdoms of men got along. In the film, the 300, the metal currency showing Xerxes’ face indicated the owner, Theron, was a traitor to Sparta.
In science fiction, power bases and economics change. Characters usually don’t grow their own food. People living on space ships or colonies have technology but not necessarily lifesaving essentials of food, water, clothes or air without someone on the outside providing it. They can’t eat or drink metal coins so the power base changes from intangibles like knowledge and security to basic supplies. In addition, energy keeps a space station going and some of the most necessary items must be imported from civilized planets.
Sometimes the important items can be things we take for granted. In Larry Niven’s and Jerry Pournelle’s book, Fallen Angels, the satellites are independent from the Luddite Earth and some of these astronauts crash on the planet. The satellite citizens forge a bond with science fiction fans to bring them back to their home and resupply some of the most critically needed items. the authors uses hypodermic needles as his example. The station controllers can resterilize and reuse them but they can’t sharpen them. Thus, new needles become important.
Star Trek (the original and Next Generation series) ignored currency, implying everyone simply got what they needed. A nice idea but bogus when facing the facts that some people in the series were still obviously richer and more powerful than others. Yet, if you examine the Enterprise society as military ship, this concept of people getting what they need holds true. The military even today does supply any essentials to its soldiers when they are abroad. Star Wars indicated a universal economic system where the same coinage had equal value everywhere. This simplified the story’s “world” so that the writers didn’t get too bogged down in details. Barter was still used, but only at the poorer levels.
Bartering was featured in the Hunger Games as well. Katniss’s District 12 folks had few coins. The mines seemed more like the old Pullman towns where people worked for the company, rented company houses, and shopped at the company stores. The debt for the family grew, turning the system into a type of slavery. The only economic exchange was outside the system, and therefore illegal, as the residents bartered what they made, owned, or hunted.
Yet space travel and economics poses other problems. Would a rebel fighter remember to include a few coins in their space suit, just in case they wanted to visit the cantina on Tatooine? Do EVA suits even come with pockets for wallets? Wouldn’t everything be based on simple fund transfers? In our age of bitcoins and electronic banking, building a coin-free society does not seem so farfetched if the society is advanced.
You can also get really creative with economics. In the movie, In Time, (starring Justin Timberlake), life minutes are the currency, and life clocks are embedded in the characters’ arms. Run out of money and you die. As you can guess, those that control the minutes are the rich and immortal.
My book, Independence Day Plague, was set just far enough in the future to be borderline science-fiction. The economic system had evolved into largely online transactions, which left a traceable paper trail. Banks still placed value on old currency but governments weren’t printing more. Therefore, the black-market horded these old greenbacks in order to provide untraceable transactions. That factor proved significant in how my protagonists moved around while staying off the information grid.
Whatever system you use, don’t have your character buying anything they need from a limitless purse without an explanation. This concept is as annoying and amateurish as the never-needs-loading gun. Poverty and desire make great motivators. Use them effectively. Just be sure you understand what the true factors of wealth are in your world. Currency may seem like a small detail but it adds to the plot or indicates specific aspects of your world. In addition, if you know what factor makes the wealthy rise above others, then you know who the true power broker is in your story. It’s up to you to make that person the friend, the enemy or the background for your protagonist.