Agriculture and Economy

Since this is something that is mostly done already, let's start with that. In most RPGs economy is entirely irrelevant, as it never comes up in the things players are actually interacting with. But in a campaign in which PCs can be community leader and most internal conflicts and mad schemes are based on limited resources, I find it something that has to be worked out with at least basic detail.

The main food crops are rice in the south and barley in the north, with potatoes being a common secondary crop. Rice is great and somewhat exotic and fits into coastal marshlands. Barley is the less boring and generic alternative to wheat, which is really associated with Mesopotamia and Egypt, and it also makes a good base for beer. And potatoes are just such an awesome plant that it just would be a shame not to have them. And since we're at it, let's also have grapes because it's hard to imagine an ancient setting without wine. And finally there's mushrooms being farmed at large scale wherever there are available caves with the right climate.
Crops are usually not exported and produced locally, as few places have a large enough surplus to trade away. The exception is wine, and barley for making beer.

The main farming animals everywhere are goats, which produce milk and cheese and also meat and leather. There are also small stocky reptiles called taung that are kept like pigs. Geese and pheasants are kept for eggs, meat, and feathers. In northern lands, people also fish large numbers of cod that are dried and salted and exported in huge amounts as food on ships.

Another important food source is honey, which is harvested from the hives of hand sized insects that nest on cave walls. It's the main source of sugar and a major export good.

Also in the realm of food is salt used for preserving food, which is extremely important for the city states, as chaotic whether and disasters can massively disrupt their regular food production. Without salt, the days of a city are numbered. It is by far the single most important resource.

If there are any contenders it is tin. The main ingredient for bronze is copper, which is somewhat more common, but the required addition of the rare tin is always the true bottleneck in bronze production. Since the population of Kaendor doesn't grow and bronze can very efficiently be recycled, the amount of tin needed to replace lost bronze tools and weapons is relatively small. Which means having only one or two known tin mines in the entire world wouldn't be implausible.
Finally there is silver. Most trade between cities and tribes is barter of goods while most internal exchanges work on credit and workers pay mostly consists of food. Where this is not feasible or inconvenient, silver is a high value resource that can be very easily stored and transported and traded for anything else without problem. Silver is measured by weight. In what shapes and sizes it comes is irrelevant. There is also gold, but it's of such a high value that it's almost exclusively used in business between city states.

Wood has almost no value in trade. That stuff keeps growing back faster than people can cut it down and nobody ever runs out of even the most specific pieces of lumber needed for speciak purposes.

Economy in towns is very centralized, with craftsmen usually being employed by the local lord who is responsible for trading the raw materials and finished goods with other lords and distributing the products among his servants and the heads of the land owning families who pay the palace back with food. People in towns and villages have very little silver as everything they need is provided by the lord of the palace or head of the family for whom they work. Travelling merchants mostly do business with these and primarily trade for goods, but anyone with some silver can buy small things from them for themselves.
The city states are more urban in nature and there are many independent craftsmen that sell directly to individual customers. Cities use standardized coins to speed up the weighing of silver, but they are different in each city. Most people have some coins, but the distribution of bread, barley, and rice is usually run by the palace and the main expense of the tax income.

When detailing the city states, I plan to work out the salt and tin trade networks to greater detail, as these are the things that determine power and international relations, and are the stuff people go to war for. There certainly will be a salt city and a tin city, and I also have a good idea for the primary cod exporter.
There are of course also various spices, textiles, dies, and drugs that merchants make huge profits with, but I don't think these make much of a difference when it comes to the dependencies and power structures between settlements. As such, I don't think they need to be spelled out.