Probably adopting a child that had a horrible life and raising him or her as your own. You would love them and provide for them and maybe they can grow up to do good things for other people too.
That is an impossible question to answer. you answer it yourself in a way when you hand over some of your money. Whether at the "Support the fight against medicare" booth, or at the "Doctors without borders" booth.
That's the trouble isn't it.. there are so many and in a way they are ALL deserving... all clearly need help or they wouldn't be asking... for me it's perhaps conservation projects... save the rainforest, tigers etc... and cat and dog rescue.. but that's mainly because kids are taken care of here.. we have charities that help kids and child protection charities.. but mostly people are taken care of here..