-Remove Vending Machines from inside of POIs - it makes no sense to have a POI locked up like fort knox with traps and sleeping zombies everywhere - yet it is powered up and routinely restocks with food. Are we supposed to just assume that some vendor is breaking in the building, avoiding all the zombies, all the traps, refilling the vending machine and collecting the dukes, and then resetting traps and boarding the place all back up again to sell the items in it?
-Elastic Microeconomy - Put in a supply and demand system that allows a fluctuation of prices based on various conditions (weather, day of the week, how much time the game has progressed, the biome the trader is in, etc). You could even tie the economy into the unique seed for the game and each game has a different starting supply and demand for different items. An example of its utility would be something like every 5-7 days the price of ammo goes up. You'd then have situations like the choice to sell your ammo at a high price or keep it for the horde. You could attempt to buy low when demand is low say on the 3rd or 4th day of the week and try to sell back, but you'd still be with less ammo for the horde. Medical demand could go up on day 8-9 and it would either cost lots at that time to buy medical items, or you could make a killing selling them.
-We need truly rare and valuable commodities. Things that are almost always in high demand and are always valuable. Antibiotics in particular should be much more valuable, rare and hard to craft than it is. It is the cure to the zombie virus and it's currently not worth much more than a few bowls of soup. A chemist who makes antibiotics should be one of the richest people in Navezgane.
-Food - it's just silly right now. Having so much food available to purchase at such low cost just ruins the 'survival' part of this game. There is little need to hunt, farm or even cook your own food due to the vast amount of routinely stocked food in all the vending machines and at the traders. The food is so ridiculously cheap - I thought it was a bug when I first saw it. Price of food should be much higher. If it were me, I'd make food have an actual nutrition mechanic and give it all a quality system. Low quality food is what you'd mostly find in the vending machines - but the high quality, most nutritious things would be expensive, and harder to make. You could make a good living selling them as good quality food that keeps you healthy would always be in demand. Low quality food could be a bit more abundant, and you wont starve if you eat it, but you won't be very healthy either. Eat too much low quality food - and your overall health starts to become affected. Eating a lot of high quality, nutritious food and you start to gain long-term health benefits that aid in stamina, and faster healing.
-Ammo should obviously be much more expensive and\or rare than it is now. You can just use traders for all your ammo and it won't break the bank. It's not until you get to the turret stage that you might want to start crafting your own to supplement for the difference. The biggest reason ammo is just so abundant is because of all the stash boxes in all the POIs combined with the trader. It completely negates the value of ammo and just leads to not even caring about reserving it like I used to. Now after you've leveled and are just in mid-game and beyond you can just run through POIs on full auto blasting them..because..why not? I can get ammo really cheap and get more and more as you go through the POIs. The ammo quota keeps rising instead of falling even when you're being trigger-happy. A constant net-gain in resources due to the abundance in loot and low cost. Minimizing the amount of dungeon POIs in the game and thus having less stash rooms while increasing the cost and rarity on traders would go a long way. I can't emphasize enough how much overpowered you get by just looting the POIs over and over - especially doing it via the quests where you have a system going where you get sent to a POI you had just been to so know it like the back of your hand..you run through get all the valuables - get ammo out of the boxes - finish the quest - sell all the valuables and then buy all his ammo. You can do that over and over with 5 traders and in a very short amount of time you already have so much weapon mods, medical items, and ammo that you're basically just playing with creative mode on at that point.
The more items you give the traders to sell by default, the more and more you could potentially nullify a lot of the mechanics in your game. So you have to keep that in mind. If you make it to where traders have all the wood, concrete, steel, you need to build a base - you instantly nullify that gathering and crafting part of the game. In one of the last experimentals before stable - I did a playthrough without any INT except for the bicycle. I was already able to build a concrete base just by the trader and looting alone. I did the quests over and over -and looted hundreds and hundreds of respawning stash boxes over and over doing that- found my iron tools, lots of rebar, concrete from the bags in the POI, etc that way -sold all the loot - and just bought the remaining concrete buckets from the traders and built a base. It was admittedly rewarding to do it that way, (in retrospect, I think it was more because it was just different than I've ever done a base before) but it was a bit too easy to do and it definitely nullified a huge chunk of the game. I think traders should lend more towards supplementary for mats than something where you can just buy everything important with all the trash you looted and cars you took apart.
Lastly, When thinking about the economy in the game - keep the future bandits in your mind. I'd look into adding a container value mechanic. Every item in our containers and backpack is already worth a set amount of base dukes. Use that system already in place and add on to it for the bandits to asses your container worth. The higher your container worth - (the more valuables you have at your base or on your person) - the greater the chance you might have bandits showing up. I know this is outside of the current scope- But, I'd love a scout bandit that comes to your base and can assess your overall container worth - the higher your container worth - the more heat - and if the heat is high enough the scout will call a raiding party. You could make certain containers like vaults and safes where the scout cannot determine all of the value. But, to counter that - vaults and safes might need to be harder to make, more expensive to buy and slower to open.