Thread: "Oh sh#t" overnight kit

Reading about some hikers stuck out overnight, and from my own recent experience with a thunderstorm that came in 4 hrs ahead of schedule, I'm rethinking my basic carry kit.

The basic philosophy behind it is I can leave my big main pack at camp or the hut and take a lightweight setup in the 20L attached bag out with me that has enough stuff to deal with weather changes and allows me to spend a rough night if need be.

Thinking on it, the reasons I wouldn't be able to return are:
Lost
Injury
Sudden unsafe conditions (for example in the thunderstorm I mentioned I had to return via a pine plantation, I heard several trees go over while I was walking, if I'd had another option I'd have camped out and waited for the wind to die down.)
Gear failure (ie both my headtorch and my backup failing)
Exhausted to the extent that continuing on for the night would be unsafe.

Due to that I've set the following requirements:
Must allow me to spend the night in freezing or near freezing conditions without use of a fire.
Be able to keep me out of wind and rain
Must be able to be done without use of light.
Be simple to set up, since I assume I'll be not in the best headspace.
Not require me to buy much more stuff, or double up on stuff that would be in my main pack.
Be moderately comfortable. I realise there are a lot of ex army types on here who could survive a snowstorm with just a doc leaf to cover their nuts, but I'm a desk jockey and appreciate some comfort

So far here's where I'm at:
Rain jacket and pants, which are for weather changes.
Fleece midlayer, wool neck gaiter and gloves plus down jacket for sleeping in.
Poncho/lightweight bivvy bag. - I'm torn here, the poncho is way more versatile, but the bag is much easier.
Sleeping mat- this is the single heaviest thing on the list at 600gm but being able to get off the ground and off any stones is maybe worth it?

This all fits into the bag with enough room for water and some food.

What are peoples thoughts? Am I overdoing it?