Just think of all those day sailors on here who fear being out after dark!
Well, it's scary out there
You forgot about lunch! You need to know how much food and bevvies to bring
My wife is pretty tolerant of my sailing, but if I didn't bring enough snacks because I packed 3 days worth of food for a 5 day trip, I am pretty sure I would be sailing on my own after that.
I frankly can't imagine heading out on any trip whether it be a day trip or a multi day passage without having at least a rough idea of how long it was going to take.