Story Event items are only used for completing the specific Story Event tasks (such as “Fix Missing Item” that requires the Stone Can), so once you finish playing each event and tap “Complete” on the respective task, you will no longer need these Event items.

As soon as you complete the task, any item related to that Story Event will turn into one Bronze Coin Level 1. Additionally, once you have attained the final item in each Story Event, it will no longer be available to play.