Great post, Bryd!
That's the beauty of a forum like this: We have the ability to bounce things off one another and learn from examining real life situations. I think the day hiker has luxury on his/her side- since you anticipate a short trip you're not already encumbered with a 50 pound pack. In my mind that means that each person carrying a 10-15 pound load is really nothing. Certainly not like humping 80 pounds along the AT!
You see articles and videos on the "Top 3/10/20 Items For Survival" but realistically we should probably think of "2/5/10 Pounds of Gear for Survival." If you take a kitchen-sink approach to gear, at best you won't enjoy your time out of doors, feeling like a pack mule. And at worst, you'll leave that bulky pack at home because
it's just a day hike... You really have to balance security with living your life.
I'm going to copy your list into a Word file for reference.