Location and conditions really make a huge difference in the amount of gear I'd take with me for a 'just in case' scenario. In general, I try to keep enough gear to survive a night out, even if it won't be comfortable. Backcountry ski trips call for a lot more food and insulation than summer trips down the coast, and if surviving the night just calls for checking into a hotel and ordering room service, so be it.
Most conditions I've toured in, surviving the night would just be a matter of pulling off to the side of the road, pulling on whatever jacket I had with me already and lying down.