The Big Knit campaign run by Innocent Drinks is happening again this year, hurrah!
People knit tiny hats for Innocent Smoothie bottles, and for each promotional bottle sold money is donated to keep older people warm during the winter. It's a great cause, and a fun way to use up some leftover yarn or to learn how to knit if you've never tried it before (as a terrible knitter, I can assure you that they're very easy to make!).
I attended a very fun Big Knit 'Knitting Marathon' last year and a few years ago had a knitting marathon of my own, knitting all of these little fellas:I was stuck in bed ill with some horrible winter bug, and knitting all those little hats kept me very entertained. I had so much fun knitting all the stripes and my mum (who is much better at this sort of thing than me) kindly made all the matching pompoms:I doubt I'll manage to make as many hats as that this year, but you never know...
Instructions for knitting your own tiny hats can be found HERE.