I know it's not brain surgery, or saving lives, but I love making a difference.
Nothing major - looking after a birthday party personally to avoid difficulties. It was bound for disaster due to a clash in our schedules, but I averted disaste skillfully and made for a really enjoyable experience...
They even shook my hand when they left (this is a group of 14 year old boys mind....) and wished me a happy new year.
I left work with a smile on my face!