I'm not generally far enough to honestly consider it an emergency but I normally carry kitchen matches or lighter. I have one of those mag and steel starters and if you have it when the emergency arrives it would be great.

But the emergency kit I consider most vital I carry right in my head.
http://www.trackertrail.com/survival/fire/cokeandchocolatebar/part2/index.html
I never really worry about it much unless I'm in a fly in camp in the Canadian wilderness or something.