To select which Fields are shown in the Wrapup Panel on the Account View go to Menu > Setup > Field Headings > History Additional Fields.

The entries in the Drop Down list are the Account Additional Fields. When selected here they also become available on the Contact History edit screen and, if selected, also on the Wrapup section.

When selected to show on the Wrapup, if the Clear option is selected the system will clear whats currently selected in the field from the last wrapup and will allow you enter something new on this wrapup. If the Mandatory option is selected the User will need to ensure this field is populated before they can save.