While, I've never made a fire on any day hike, I'm prepared to make one if ever needed. Here in the PNW, even marked trials can be pretty remote and some are not well maintained and thus do have places where it would be easy enough to fall and suffer an injury. Storms too can cause windfall that requires getting over/around and a fall could easily happen. I've been on trials in the Olympic National Park both on foot and horseback, close in to trail heads, where you can go from relatively bug free to literally swarming with mosquitoes, usually when the trail takes you into a low brush covered wet area. Lots of times those areas are also wet and can be slick in spots even in the summer. So it sure wouldn't be that hard to get into a situation where injury could happen and being prepared to spend the night is a very good idea, even on marked trials and staying well within the parameters of the location that was given to a responsible person in case you don't check in by a given time. Doing everything right you still could spend a night out, even if searchers had your exact location.

I can think of two areas fairly close to me that when you pull into the trail head parking area, different trials take off in several different directions, so even if there are a few cars, it doesn't mean others will necessarily be on the same trial.

Granted carrying a few supplies does add a little weight and bulk but it sure would make a huge comfort difference and maybe a life-saving difference. I always carry a little water even in areas where water sources are plentiful as if I were immobilized I'd have at least something while waiting to be rescued. Having a little would be better than none. Even if you're not cold to the point of getting into a dangerous situation if you're wet cold and miserable it's likely going to impact decision making. Same goes at night without a light source, panic can take over.

The only situation on a day hike where I'd go for the ultra light approach would be if I was with a decent sized group and pretty close in to the trail head. I'd still have some first aid supplies, as well as a few daily carry items, as depending on others to have anything useful can get one in trouble. Almost all of the lighter FAK's suitable for packs are lacking in adequate blood stopping supplies such as pressure pads, non-sticks, etc, so I always add a little to my kits even the AMK's. One little 2 by 2 guaze pad isn't going to do much and if you don't have some non-sticks to put next to the skin first before adding the padding it's going to be really unpleasant when you remove it.

Another thing that I do is look carefully at weather reports always before going out. Just because it's perfect when you set out doesn't mean a storm might not be coming in during the night or the next day. Granted unexpected weather events happen but at least prepare for what is in the forecast as well of knowing what night time temperatures are going to be at the location and elevation.