I've actually been thinking about this a lot lately and trying to come up with a "plan of action" for when I feel like I'm starting to slip and get overwhelmed/depressed/anxious. Always looking for new ways to cope but these are the things that have been working for me so far :

* Becoming aware of my thoughts - taking a step back for a moment and recognizing my thoughts/emotions
* Bringing myself back to the moment. "If you are depressed, you are living in the past. If you are anxious, you are living in the future. If you are at peace, you are living in the present." - Lao Tzu
* Distracting myself with an activity/task and keeping my mind focused on something other than whatever is going on in my head.
* Talking to a friend.
* Buddhism/Chinese philosopher quotes.
* Getting fresh air and a change of scenery.
* Practicing gratitude. Thinking about all of the good things in my life that I am thankful.
* This quote by Lao Tzu from the Tao Te Ching - "As the soft yield of water cleaves obstinate, so to yield with life solves the unsolvable. To yield, I have learned, is to come back again."
* Going to the gym or a for a walk and sweating out my emotions.