All your items are stored in your Inventory, which has the same sections as the Store.
The Store and Inventory are combined in a single window with two tabs. If you lack an item in your Inventory, just switch to the next tab to buy it in the Store.
Almost all game items found in the Inventory can be both purchased and obtained in the game.
You can filter items that are activated from the inventory by checking the Usable box.
The New ribbon indicates newly received items. They can also be filtered by checking the corresponding checkbox.
There is a search field at the bottom of the window that allows you to find an item by name.