Final answer:
In a tickler file, three key items to include are the date of the task or event, a detailed description of the task, and any associated documents or action items.
Step-by-step explanation:
A tickler file is an organizational system used to remind or ticket future tasks or events that will need attention. Three important items to list on a tickler file include the date of the task or event, a detailed description of the task, and any associated action items or documents required for completion. A tickler file is useful in managing tasks and ensuring deadlines are met by providing a systematic way to review upcoming obligations.