World's End and a day of two flasks. 

I forgot to pop the button on the top of mine and it emptied itself into my rucksack, and also wetted other people's sacks while we were on our way. 

Fi's flask rolled down a steep pine needle covered slope and disappeared. She was going to abseil down and get it, but we couldn't see where it had gone and she decided that the terrain was too horrible to bother.