I thought it was on this forum, but it must have been the previous one, that there was a discussion about the self-heating Wolfgang Puck coffee cans that were on the market. I remember posting about trying them in Groaning (cave temp 39 degrees) and how they didn't work worth a darn in a cold cave environment.
Well, if you didn't try them, it's too late. They've been recalled because some of them exploded:
http://www.realtechnews.com/posts/3028
http://www.bevnet.com/news/2006/04-28-2006-wolfgang_puck_self_heating_cans.asp