A while ago I found this Ortovox Gemini Double Emergency Shelter, but I think one person might have a hard time breathing... But maybe that's not the right picture, because the single person one looks the same.

Edit:
Oops, first post and already made a fool out of myself: You can put your head through the hole and use it as a poncho, but there's a big opening at the "bottom", so both people can breathe.