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:
Poncho
Space-blanket bivy sack
A small roll of light line
Matches
Firesteel
Mini-bic
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
Light gloves
Fleece beanie
First aid kit
Spare medication
Sunscreen and DEET
Headlamp
Small LED flashlight
3.5" folding knife
Whistle
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.

