I have been meaning to get around to doing this for a while, and now is as good a time as any. So far, I am thinking:
water
blankets
cereal bar type snacks/ chocolate etc
first aid kit
disposable urinals
torch
wet wipes/tissues
Part of me thinks summer car kit, should be different to winter, but then things like finger warmers could just be left in the car. I'm thinking of scenarios from being stuck on the motorway for hours (as has happened a few times to people where I live near the M5) or being stuck for a while down a lane waiting for the breakdown service, as happened to me last year.
Any other ideas?