Part of me would love to leave it to someone totally random - like, on the third anniversary of my death, someone is to the stand on a particular street corner at 1pm and give it to the 17th person who passes by. Just for the sheer joy I would have if someone gave me money in that way!
In reality, I'd probably spend a fair bit while I was alive, shopping locally and buying green etc, because I think that's a good way to pass it on to the next generation; I'd also be one of those old ladies who shakes your hand and leaves a tenner in it.
If there were particular people who'd stood out to me in life, I'd leave them some as a surprise. And then I'd leave the rest to charity, I think.