This article from the Mayo Clinic talks about how exercise can help ease depression and anxiety by producing mood-enhancing chemicals in the brain. Thirty minutes of exercise three times a week is ideal, but just ten minutes of exercise can help in the short term to improve mood.
So what do you do for exercise? You can take a brisk walk around the block. You can remember what you did in gym class in high school: ten sit-ups, ten push-ups, ten jumping jacks, jog in place for two minutes, jump rope for two minutes, lift weights for two sets of ten for each set of muscles.
Maybe I should take my own advice and do the things I just wrote about. :)