Items in Supercity fall into two big categories:

1) Items that are added to your inventory and can be used in the quests later.

Where do you receive them?

Wherever you receive them, you can stock up on them to have them handy in case they are needed in future quests.

Example:

Please, keep in mind that the amount of each item you can have in your inventory is limited. If you can no longer produce or receive some items, check if you have too many of them by looking them up in your inventory. To do that, start typing the name of the item into the search field:

If you have too many, you can sell them by clicking on a cashbox icon:

If the quest asks you to have a certain amount of these items in your inventory, the amount you had before this quest started also counts. Once you have enough of these items to complete a quest, click on the "Use" button in the quest, the items will be spent and this part of the quest will be marked as Complete. More about the "Use" button in this article: https://playkot.helpshift.com/hc/en/4-supercity/faq/849-use-button

If the quest asks you to produce/collect a certain amount of these items, only the items that you produced during this quest count.

Sometimes such items start dropping only when you have a specific quest.

2) Items that are not added to your inventory and can't be saved up for later quests.

When you produce a crop of potatoes at the Farm. For example, you don't receive the actual potatoes, you receive only a certain amount of goods:

If you have a quest that requires you to produce a number of potato crops, then every time you produce potatoes at the Farm, they will count toward the quest, but still won't go to your inventory:

These items are produced whenever you start the production in any of the building from this list: