The Item Box is used for storing items that are not needed by the player. Items are deposited directly from the player's Inventory.
Early Resident Evil
Introduced in the first Resident Evil, Item boxes are usually found in safe rooms along with Typewriters. Characters can only carry a small number of items at any given time, which makes inventory space valuable. The Item Boxes allow the player to deposit unwanted items such as key items that are not yet needed or weapons that are out of ammunition. In nearly all games item boxes carry the same items no matter which one is accessed. Resident Evil: The Director's Cut and REmake's Real Survival mode removes this function, but the overall function remains the same. In some games, items from past playthroughs or things left by other characters are placed inside upon the playe's first encounter with one.
In the early games of the series the player is not able to freely drop items outside of item boxes unless prompted by the game. Resident Evil 0 was the first game to allow players to do so, and so the item boxes were removed.
Item boxes do reappear in games that retread events of older games in the Raccoon City Police Department during the "desperate times" scenario in Outbreak File #2. However, they are inaccessible.
The First Revelation feature a Weapon Box to stores only weapon, only 3 weapon can be brought at a time.
The second revelation does not feature an Item Box, as they use the mechanic of leaving items on the field like RE 0 and Outbreak. Weapons however can be accessed and switched via the workbenches scattered throughout the game.
Modern Resident Evil
The concept seemed to return in Resident Evil 5 in the form of the Item Management screen, which run on the "buy & sell" mechanic like RE 4.
Resident Evil 6 does not feature Item Box, any unwanted items need to be thrown away. Key items will be stored separately.
Resident Evil 7: Biohazard, the Resident Evil 2 remake and the Resident Evil 3 remake revived the Item Box from the early series, which the player can use to store weapons, health and even key items. All three games will place any unlockables in the Item Box.