Apologies for an amazon link (not a fan of space d***s) but just to see the prices...
https://www.amazon.com/Emergency-Blanket-Survival-Thermal-Sleeping/dp/B01M4MXEQO
One of those, dressed, 40f degrees = too hot, so I stripped = still too hot. They reflect like all of the body heat, are paper thin, fold into a 4"x4"x0.5" square, somewhat durable but everyone should have 1+ in their "whups I'm stuck in my car" bag. If you have food in your stomach and/or body fat you will not freeze.
First off, try to stay calm and don't rush. Keep it slow to avoid slipping. In rough terrain in the dark, sometimes the best thing to do is stop and wait until morning. Don't try to keep going if there are lots of loose rocks or climbing is involved or you can't clearly see the trail anymore. There's a chance you might go down a deer trail on accident and get lost or hurt.
If it gets cold and you have no way to light a fire and no proper clothing and no space blanket, try to find a spot sheltered from the wind and use dry leaves as a blanket, maybe stuff them in your clothes. They have to be dry, not wet or damp.
Being prepared before you head out makes it so much easier. If you have a light on the hills, people might see it and know to look for you.
Basically everything you mention sits in my front trunk, plus:
The "granny lead" mobile charge cord.
Tire patch/plug kit - sometimes you can patch a tire just as fast as using the can of fix-a-flat, and plugs are a permanent fix. (The exact one I have isn't sold any more, here's an article about them.)
"Person" roadside kit:
First aid kit
$30 in small bills (maybe add a "non-expiring" prepaid $20 Visa for if you get to a charger that takes credit cards and you've lost your wallet.)
Wind-up Emergency radio - There are many to choose from, this was just the first Amazon result.
Emergency food ration bars - They taste like the food definition of "meh", but they're shelf-stable for 5 years in the temperatures a front trunk will get.
Emergency water packets - water in temperature-proof containers that can withstand being frozen.
The last two can also frequently be found at "military surplus" type stores.
In case you can't tell, I live in an area with regular "impending natural disaster", so I keep "preparedness" stuff in my car in case I'm stranded and services aren't available.
can you get those foil emergency/rescue/"space" blankets?
One of those between two blankets and you'll probably be sweating.
I'm biker in Japan, and I'm using a Space Blanket for fix the items and insulation. https://www.amazon.com/Emergency-Blanket-Survival-Thermal-Sleeping/dp/B01M4MXEQO It's not that expensive so highly recommend:)