Currency emerges whether people want it to or not: the natural forces of the market make people adopt it due to the benefits it brings to markets. A market without a currency lacks one of the most important aspects of free trade: the ability to gather information on the value of goods through unambiguous prices. Currency emerges in any market naturally. Once again, prisons are the absolute best example. There would, however, likely be many different, regional currencies. One are that uses dragon scales might border another that uses bottle caps, for example, and the forces of conglomeration would be slow in a deregulated world.