The hour and minute fields can be removed. You can set which hours and minutes should be selectable.
The departure field can be replaced by a billing unit select. Your guests would only have to select how many nights they want to stay.
All reservation fields can be replaced by hidden fields to either dictate them or take the value from the widget and search form.
Many options like restricting the amount of adults can be set directly at the form field.
A simple custom field.
You can replace them with real ones added under settings -> custom.
They have more options and can be displayed when adding a reservation as admin