There are plenty of gadgets you could wish for as you're sitting in the dark on a bus stop, with a dead phone, in freezing temperatures.
I could tell you to pack emergency charger, a supply of hand warmers, or any number of other supplies every time you venture out — but if you're like me, you will either eschew them out of laziness or forget them entirely when you really need them. Another option: a tiny aluminium canister that does triple duty as an emergency USB charger, a torch, and a hand warmer that warms to 40°C for three hours.
It's no replacement for real survival supplies, but as in-a-pinch winter gadgets go, you could do a lot worse. You can pick one up for $40 (£25, without shipping to UK) —throw it in your coat, or the coat of your perpetually unprepared loved one — over at Cool Material.