Im leaning towards two currencies, some kind of official money used by the cities/evil company, named something like royal mark/chip. Most likely metal or plastic coins.

In the wastes another currency (but the currencies may be traded with eachother maybe). Maybe gems. Mineable in the desert and has traditional value. VERY hard to forge. A more or less standarized size of ANY gem will count as value 1. Larger gemstone are broken down into stones of value 1. Not entierly realistic maybe but may work nicely gameplay-wise.

Feedback?

In the event of a zombie apocalypse, the survival of paper money seems highly unlikely. The coins that supplement the paper money, though, seems a lot more durable. Coins like pennies, nickels, dimes, quarters are common in North America, and would still be common enough to exist after your average apocalypse, even if there's no continuing production.

Though in a more realistic setting, I would be concerned losing a hand or two getting a result like this out of coin ammo:

The thing why I don't believe coins would be too successful is that they have no real value. They are of course much better than paper money, which merely has the value of toilet paper (any other value that it has is purely based on a promise made by your government, which already isn't worth a lot now but surely is worth nothing in a zombie apocalypse).

You can eat tuna cans, but you can't eat (well, you sure can swallow, but to no avail) nickels or dimes. The rare metal in them is not really all that rare, so there is not much of an incentive hoarding them for "better times" when society has been rebuilt, 10 or 20 years later. Other than for example gold, they'll be pretty worthless. But even gold quickly loses its value when there is nothing to eat around. In order to carry a noticeable amount of money, you would have to carry dozens of kilograms worth of pennies.

Now, canned tuna, or ammunition, or even clean bottled water is not particularly valuable either -- to us. But they all have a huge situational value when there is nothing to eat, only reeking water, and lots of zombies that want to kill you. Nobody will trade a pair of shoes for 20 kilograms of coins when the winter is nigh. But he might as well risk cold feet for six bottles of water or two dozen rounds of ammo.

I think in the case of a Zombie apocalypse then something like dried zombie fingers would work.

I like this one, small societies could start accepting them, because if they do they would be rewarding people for killing zombies(and taking their fingers) giving the society some kind of safety.

off course, a society creating any kind of currency without intrinsic value(anything that is not consumable) would need some kind of internal functioning economy making enough profit to pay for these fingers, and it would take a while before the currency wouldn't be so dependent on certain (official) backers.

Paper money has followed the same route, in the beginning it was backed by a promise of gold but after a while that would no longer be as necessary.

(UK still prints this promise on it's currency but no longer holds the promise)

Another idea is some kind of bitcoins, a post-apocalyptic world would not necessarily have lost it's satelites, and only the traders would need the hardware to access the bitcoin-network. Off course it would kill the trade between non-traders/players.

Some things to think about:

Do you want the value of goods/currency be "set" in advance of creating the game-world, or do you want an open economy where supply and demand dictate their values ?
Do you want goods to be created or maybe even be in unlimited supply by (NPC-)traders ?

Do you want currency to be created or maybe even be in unlimited supply by (NPC-)traders ?
Or would you prefer the game world to always hold 100(or whatever) units of currency per (active)player ?

You are thinking WAY to realisticly about this decision:) The game is more along the lines of diablo...

Gameplay-wise and how the world works is more important than what money actually is and how it would work in real life.

Good questions powerneg!

1. Value of money and almost all items will be fixed. Maybe some vital trade goods like medicin can be supply/demand but i dont want the game to turn into a trading and transport game.

2. NPC-traders will work like in diablo. They spawn some items. These are refilled/replaced over time.

3. NPC-traders have limited money. So you may not be able to sell all your loot at the same place. However, if you buy from a trader, that "cash" is added to the traders cash.

4. No word-wide limits on currency. Not needed for my game and hard to balance. Also, its single-player

But if you buy 50 ammo that must logically cost more than 50 ammo casings (if ammo casings are used as currency for each ammo fired you get "one money" back).

So you will have to carry around ALOT of depleted ammo :) Not so practical.

But if you buy 50 ammo that must logically cost more than 50 ammo casings (if ammo casings are used as currency for each ammo fired you get "one money" back).

But I still like the idea, it's actually a nice one. Casings have a lot less weight than full rounds, and while they are useful (make new ammo) they are at the same time not immediately useful.

It may also bring a new angle of resource management into the game. You can keep ammunition for use, or you can disassemble/fire it if you need a big amount of money for buying a larger gun or such. Then you can use it to buy stuff, but now it isn't good for killing zombies any longer. Which makes your journey to the merchant (with only a few operative rounds left in your pocket) more of a challenge.

There is a sci-fi movie but I can't recall the title... The idea there was that people at age of 25 stopped aging further. Instead everyone had a timer embodied (implanted?) in their wrist that activated at the 25th birthday. You then had 1 year of time left until death, but the timer also served as currency. You get paid in time and buy everything for time.

In poor district people rarely had more than few days on timer and it was common to knock someone down and "steal" their time.

If you want to add that kind of pressure to player and discourage idling in town you may want to implement something similar. Although you may need to change the way people get such timer as implanting on birth doesn't make much sense in zombie apocalypse ;)