If you are really desperate, I've heard of people grabbing those chemical heating packs from Army disposal stores and keeping those ready for such an emergency
I did a quick search for them and unfortunately only came up with this dicky looking one
50 degrees in a few seconds isn't that bad, and re-usable! There are probably better ones that last longer out there...beats me
http://www.latestbuy.com.au/hot_packs_lifestyle.html 
