I have a playlist for when I'm not feeling particularly chipper, filled with Queen and Bon Jovi songs, which never fails to cheer me up. There is something very satisfying about singing along to Livin on a Prayer, amongst others. It's worked for me since my GCSE exams, and it's become a habit of sorts grounded in nostalgia - the songs remind me of the feelings I had when I'd finished an exam, which makes me feel better...weird as that might sound.
I also find playing a Dynasty Warriors game helps. Wading through hundreds of enemies causing general mayhem is extremely good for frustration.