I also agree with Aimless. I have helped teach Basic Mountaineering for some time. The "culture" (if that is what you call it) among the instructors, some of who are SAR members, is that you carry the 10 essentials always and learn how to use them. I see lots of day hikers on popular trails in summer with nothing but a water bottle, if that.
It is a free country and they can do what they want, but for me and my friends it would be unacceptable if you are hiking/climbing with us and that just happens to be the way we have been trained and what we do. Besides, part of the reason i day hike is to get in shape for longer hikes. Why not carry a few extra pounds and get used to it?
It has been fun on a few occasions to have a tarp to sit under hand have lunch during an unexpected rain shower. If you live in the Pacific Northwest you lean to take rain gear if you intend to get very far from the car.