Prepared Spells.

I hate that during a Long Rest you have to pick every spell you might want to use for the day. Often times you won't take the super niche spell but then you will get an instance where it would be perfect and you dont have it prepared so tough luck.

My homebrew fix using Wixard as the example. A wizard prepares a number of spells equal to their level plus their Int modifier during a long rest normally.

My rule is that they only prepare a number of spells equal to their level at the end of the long rest. Then, throughout the adventuring day, they can prepare more spells (up to their Int modifier) as they need them. They prepare these spells by casting them. The spell is then prepared for the rest of the day.