Pay it Forward!

This. Just... What he says. I've had it happen to me once or twice, done it when I could, and it really does brighten up your day, both the person doing it, and the person on the receiving end. It really doesn't have to be a big thing, it could be as simple as helping someone get something off a shelf they can't reach, or if they're short a couple cents, help them out. Even lending a shoulder if someone's having a bad day. Something.

Anyway. Pay it forward.