From Brotato Wiki
Item
Crown is an in-game item that can be bought from a Shop or can be found in a Crate. Most Items modify the Stats of the player, and some of them provide additional effects.
Unique
Crown is a unique item. Only 1 of each unique item can be equipped, and it will then no longer be offered in the Shop, and no longer drop from loot crates.
Crown
The Crown increases the amount of Harvesting you gain at the end of the wave by 8%. The Crown can provide large amounts of harvesting if found early. See the Harvesting page for more details.
Note that the Crown stops functioning after wave 20 when playing Endless Mode as the Harvesting Skill begins to decline.
The Crown is particularly powerful on characters with high amounts of Harvesting, such as 
Farmer or 
Entrepreneur.