The economy is entirely player run. It relies heavily on players to gather resources, craft necessary items and trade. Players can barter or buy and sell using local currency.
Town and individual bank accounts.
Towns can impose taxes.
Town quartermaster can collect resources and goods.
Player run shops and auctions.
Players post want ads to increase demand.
Resources can be controlled and destroyed to reduce supply.
Trade between individuals and towns.
This will start off with simple player bartering / trade. We will add trade totems to allow players to set up offline trades. Tribes will be able to set currencies based on common items. Object decay and loss of quality as well as resources limited to certain areas should help to drive trade and the economy.
It will definitely be a barter-style economy at first. Players will be trading things they don't need for things they need. However, over time, players will discover what some of the most essential materials are, and those will be established as a kind of currency. And, moreover, that could very well change based on supply/demand.
For example, nails could end up being in high demand, thus everyone will be wanting them and trading to get them. When that happens, nails will become a kind of currency. People will say things like, "I'll give you 50 nails for that X." The beauty about this game is that the developers aren't setting a currency, and therefore the value of resources and items will not be set either. And, since there are no NPC vendors (thank God), there won't be an infinite supply of resources with a base price.
It all comes down to simple economics. For instance, if the developers introduced an NPC town with a vendor you could buy skulls from for 20 nails a piece, this does a deservice to the game's economy. Why? Because then the price of skulls could never be higher than 20 nails--forcing players to sell them for 20 or less. It's going to be very interesting to see how the player-driven economy grows and evolves.
I see things harder to find/make being a currency beyond the barter system. Perhaps only scavenged items like bottle caps.
It will be really interesting to see if actual currency will become that in game based on our preconceived notions. Maybe nails will be, who knows. I find it interesting that the abstract concept of "money" is replaced by the barter system when things are "primitive" like thet are now or when inflation is out of control.
Nails won't be currency and there's a simple explanation, you don't use money in crafting. We may use it as a base value, and build currency system around it.
We'll some day run out of scavenged nails and have to craft them, and their value will most probably change.
I'm guessing $, beer tabs, bottle caps. It's the most obvious choice.