If the idea is to survive an unplanned overnight, then I suppose I should just list what I normally take on a day hike - but when it comes to that, I never count the items I bring with me; I just think about what it would take to survive if I had to stay out overnight, which varies depending on the expected weather and the hike location.

Long ago I noticed that most day hikers were woefully underprepared for an emergency night out and I now habitually pack for that possibility, no matter how familiar or populated the trail might be. I don't take enough to be especially comfortable, but I'd almost certainly survive the night.