Forseen Spell

Your Divination abilities have grown to the point where you can predict which spell you will need. When preparing/memorizing spells, leave one blank, or write  "predicted" counting as one prepared spell.

At any time during the day, you can instantly replaced "PREDICTED" with any spell you know but did not prepare.  You could for example wait until you come across a door, then say "I predicted this and prepared the spell Knock".

This selection lasts until your next long rest, allowing you to cast it as long as you have unused slots.  You can not change the spell once you select it.  You can not take this feat multiple times.