My first unplanned night out occurred when I was 16 and on a one week backpacking trip with experienced people. My tent got wet and, since I didn't understand hypothermia, I'd have died that night if I'd been alone in the tent. I spent the following night sitting in front of the fire, in the rain, under a poncho. Dozed off and when the fire died down I'd wake up and add some wood. That's when I became sold on the usefulness of a poncho as an emergency shelter.
Second time, age 17. My parents dropped me off after church to go looking for a lake. It took me too long and darkness overcame me in dense forest on the bushwhack portion of the route. I had enough overnight gear to light a fire and lay down beside it until daylight.
Third time was age 42 on a forestry job. I was returning to camp by a different route and found myself blocked by a cliff with darkness approaching. Spent a very boring 12+ hours of total darkness on the side of a remote British Columbia fjord in late November. Did have a fire for a while. It was ineffectual given the working gear I was wearing.
Recently I've decided to practice using my overnight gear. I've only gone out twice so far but plan to do one per month. They are long, long nights in the dark, I can tell you that.

When hiking in damp weather, I carry spare dry socks and thermals. The amount of emergency gear I carry depends on whether I'm alone, and the conditions.
I think that, when we're alone, we should have some minimum of proven equipment on our person, with the remainder in the pack.