I love music. It can completely change my mood. One of the best happiness hacks that I've stolen from Gretchen Rubin is a Happiness Playlist.
I put this on whenever I just need a boost -- before a big presentation or interview, on my commute home after a rough day or just on those mornings where you are moving too slow. Extra bonus is that creating it is fun, too.
Here is mine. Feel free to steal, or I'd love you to share yours!