From Team Fortress Wiki
The backpack is a player's personal inventory, allowing for storage for all in-game items. Items are kept in individual slots and can be viewed, moved or deleted from within the backpack interface. Additionally, most tool items can only be used from within the backpack. Items are displayed as pages, with each page displaying 50 items. The backpack can also be sorted by class, rarity, and type.
The backpack was introduced into the game with the first unlockable items from the Gold Rush Update in April 2008, with its initial storage capability being only 50 items. The storage size has since been increased on multiple occasions, and as of the Australian Christmas update in December 2010, the backpack now consists of 300 slots (or 6 pages). The Australian Christmas update also introduced the Backpack Expander tool, enabling the addition of 100 more slots per use to a total of 1000 backpack slots. Free-to-Play Team Fortress 2 players will be limited to a single backpack page (50 slots); once they become Premium players with any in-game purchase, their backpack is upgraded to the standard capacity.
Items, when moved within the backpack, will make a distinct sound based on the properties of the item itself; a distinct sound is usually heard when an item is picked and another when it is put down again. For example, the Eyelander when moved will produce the sound of a sword being drawn, and Bonk! Atomic Punch will make the sound of a pop top opening when it is picked up and the sound of a soft drink can falling to the ground when it is put down. Some items have unique sound effects, such as Ze Goggles, which make a sound that resembles the goggles turning on and off. Noise Makers will play their sound effects.
- The autosort function will not work when a user has more than 520 items.
- Occasionally, due to various reasons, items may become "invalidly placed" when placing an item on top of a different item so that one of the items disappear. (Note: The item is not gone from the backpack. The player must then move around items to make it reappear.)
- With "Show quality colors" toggled on, if you drag an item into invalid space (Off the border, into the header) The item will reset without its quality color. The quality color will return when you switch the page or highlight the item.
- When "Show quality colors" is enabled, the name of the item in the icon will not be visible in the equip menu or crafting menu. However, this does not matter as a box appears with the name along with details of the item.
- You can receive items via Steam trade (not in-game) even if you have your backpack full. New items will not be shown in the game's backpack and can't be used in crafting but can be used in game and can be viewed in the Steam inventory. If you remove/trade enough of other items and resort backpack new items will be fully available. Note that sometimes new items can be removed from backpack with no warning after entering a game.
- When dragging an item to another page, the pop-up will display the wrong item in relation to where the cursor is.
- When sorted by class, the class order uses the internal order (which is the same as Team Fortress Classic) rather than the more familiar role-based ordering.
Pre-Mann-Conomy Update backpack icon.
- ↑ Post by Tony Paloma (Valve) in thread "Item servers are down.....", Steam Users' Forums, November 16, 2011. Accessed December 2, 2011.