My worst case scenario is getting stuck out overnight on a day hike, with a cold and probably wet night. My backup is a poncho and an AMK bivy-style space blanket. If I can't pitch the poncho, I can wrap it around me and hole up under a tree or behind a rock. If it isn't blowing, I can make a bed of evergreen boughs or leaf litter along with my pack for insulation, pitch the poncho and climb in the bivy sack with all my clothes on. If possible, I can build a fire too. I do know how to make emergency shelter from forest debris and branches.
Any time I step off the pavement I have the following with me:
Space-blanket bivy sack
A small roll of light line
Tinder Quick tabs
A spare layer appropriate to the season:
*a Power Stretch vest for "height-of-summer" hot weather
*a Power stretch hoodie for the next step cooler
*a synthetic insulated jacket or vest for slightly colder stuff
First aid kit
Sunscreen and DEET
Small LED flashlight
3.5" folding knife
Map and compass
I would usually be wearing a long sleeve base layer top, synthetic pants, windshirt and a Tilley hat, briefs, socks and low-top hiking shoes. It I'm taking off on a predictably rainy day, add a rain shell and pants. There is a spare pair of socks in there somewhere.
I think the kit listed above would give anyone a fighting chance in moderately, cold weather and more so with a fire possible. If I were going above treeline in winter conditions, I would be adding a lot more insulation and shelter options.
And someone always knows where I'm going and a return/check-in time.