TF2 usable items will help to unlock some action in the game. This is an extensive list of different things that can be used by players to get a result. While some of the usable items may have a limited number of uses, others call up the activation menu once they are selected, so you should only use these items in a safe place.
A lot of usable items can be obtained in Mann. Co. Store, other things can be founded from the crates or during the game. But you can find all of the usable items on DMarket for the best prices.