The humble Task Lists offers a flexible way to identify things that need to be done. Even the paper version or manual art of listing things to do in the calendar page of a future date is quite effective.
Electronic equivalents like the Task capability of Microsoft Outlook® provide additional capabilities in that you can configure "Reminders" so that your computer or even hand-held diary alerts you of pending activity.
The method with regards to Task Lists is simple: As requests land at your feet, you quickly appraise the request and then generate a Task to manage the response appropriate to the request. You can also use the Task List to track items you have requested of others.
An extension to this method is the activity of blocking out future parts of your diary to "address" or "review" a request. If you are using the electronic equivalents, another little trick is the use the body or notes area of the Task Item to make comments about your activity. You also might choose to note when you received the request or what you asked of whom and by when. In this way you have a "mini-journal" of your related activities that can be reviewed later reducing the time you spend coming back up to speed. Have you ever found yourself asking "when did I send that" or "what did I say to him"? The notes inside your tasks can help elevate that problem.
