In Anno 1800 a huge emphasis was placed on the use of special buildings such as the Trade Union or The Harbormaster's Office. Placing items in free slots offers passive bonuses for buildings that are in the field of action, which often gives a lot of benefits and greatly offloads our economy.
To purchase items/residents for buildings or on ship boards it is necessary to complete side missions and send ships on expeditions. After completing side quests (marked with stars), we often get special items or we are joined by a unique resident who provides a bonus when placing him in the right place. Side missions are completed at lightning speed, so they should always be performed, because the bonuses offered by unique items cannot be overestimated.
In expeditions, our ship also has a chance, for example, to save a special character who will join the crew and provide a unique bonus to the ship during the expedition. It is worth to view the list of our items from time to time and constantly add them to the buildings that bring the highest benefits for you.