Project ZomboidGuideLoot rarity is ten dropdowns on your dashboard, one per item category, each running from None to Abundant. Changing them is safe: nothing is deleted, and…
Loot rarity is ten dropdowns on your dashboard, one per item category, each running from None to Abundant. Changing them is safe: nothing is deleted, and everything your players already found stays in their hands. One rule to know: new rarity shows up in places nobody has explored yet. Areas your group already searched keep whatever they had. Settings apply on the next restart after you save.
Each of these is its own dropdown, so you can make ammo rare while food stays plentiful:
Food, Canned Food, Melee Weapons, Ranged Weapons, Ammunition, Medical Supplies, Survival Gear, Mechanics, Literature, Other Loot
Food covers fresh food that can spoil; Canned Food covers canned and dried goods and drinks; Ranged Weapons includes weapon attachments; Other Loot is everything that does not fit the rest.
Every category uses the same scale:
None: the category does not spawn at all
Insanely Rare: nearly nothing (about 5% of normal)
Extremely Rare: scraps (about 20% of normal)
Rare: scarcity is the challenge (about 60% of normal)
Normal: the standard loot amount
Common: comfortable (twice normal)
Abundant: shelves are stocked (three times normal)
Open your server's settings and find the loot dropdowns.
Set each category to taste.
Save, then restart the server.

The game rolls loot for a building the first time a player gets there. That roll is baked into your save, so changing rarity afterward does not re-roll explored places. Your new settings apply everywhere your group has not been yet, and the map is huge, so in practice: loot up, then push into fresh neighborhoods.
Loot respawn is off by default and separate from rarity. It can be turned on through the Sandbox Overrides box at the bottom of your settings, one line per setting, for example:
HoursForLootRespawn = 168That respawns loot in town containers every 168 in-game hours, in containers that have been looted at least once. Buildings your players barricaded or built in are left alone by default. The override syntax is covered in Change Any Sandbox Setting; message us if you want a full respawn recipe for your playstyle.
Restarting again and again. Restarts apply your settings; they do not re-roll loot in explored buildings.
Setting everything to Abundant to refill looted areas. Same rule: explored places keep their contents. Head somewhere new.
Restarting without saving. Settings apply on restart, but only after you hit Save.
Ping us on Discord or open a ticket and tell us how survival-y you want the run to feel. We will suggest a category-by-category spread.
Every sandbox setting from the dashboard, including Sandbox Overrides: Change Any Sandbox Setting
Fewer working cars is its own set of settings: Tune Vehicle Spawns, Condition, and Gas