This is free-form. You can put anything you want into this, or remove
it from planner-day-page-template
entirely. Some people use it
to keep track of their plans for the day with tables like this:
hh:mm | hh:mm | activity hh:mm | hh:mm | activity hh:mm | hh:mm | activity
Remember, Planner files are just plain text. You can add new sections or remove old ones, or use the suggested sections for entirely different activities.