My second Night Photography Experience Evening, was last night and apart from one attendee loosing a couple of fingers to frostbite (this may or may not be true) the evening went rather well.
Thankfully I'd noticed the day before that Saints were at home that evening so I'd pre-warned all 11 attendees that traffic might be a issue. Only one was late and she'd come all the way from Surrey so we'll let her off.
We did actually loose a few people before the end of the evening... One was due to a dead battery (always bring a spare) and two more needed to warm their hands on cups of hot coffee!
Probably the best accessory you can buy for cold night is a good pair of gloves that not only keep you warm, but that you can also operate the camera with. You will thank me for this advice. :)