The only person I know personally who spent an unplanned night out was my dad. He was on a mountaingoat hunt in a rugged area near Wrangell, AK, and he or his buddy got a goat late in the day. They didn't finish taking care of the carcass until it was too late to make it back to camp, so they camped under a tree using what they had: old-fashioned wool clothes, working-man's Helly Hanson raingear, two great big frame packs that they slept between, one fresh goat pelt, and lots of insect repellant. Oh, and some molasses cookies & water for dinner.
Other than that, I've spent one quasi-unplanned night out... one trip in Alaska we found that our boat, the only ride we had back to town, was high & dry with the low tide. We had to wait until morning to catch tide back out, but we half expected that to happen anyway and planned accordingly. We had all the gear we needed, especially with the extra food & water in the boat.
Edit: In light of the OP's aim, I think my dad's experience basically boiled down to them getting lucky. He'd probably tell you that they were young, dumb, and unprepared for the situation, especially given how cold & wet the climate was. One nice thing about modern equipment is that it's so much smaller and more reliable than it used to be; there's no excuse to leave the basics behind. Dad would've appreciated an LED that wouldn't die after two hours, unlike the old halogen headlamps. He probably would've walked instead of hunker down.