That's I mean when I say "overnight gear" for a day hike. It's doesn't have to be a sleeping bag and tent, but it should be enough to survive with a greater degree of comfort than nothing.

I generally take at least my fleece bag and/or an emergency blanket or two. When it's cold and I'm going bushwhacking where I'd be hard to find I take a full backpack setup with a couple days of food in it. I'd feel pretty stupid if I got stuck and didn't have it.