One of the things that i ALWAYS love doing is going to a craft store like hobby lobby or michaels and buying something to do...Make stuff to decorate a room or something. They sell styrophome (sp...lol) squares and rectangles and stuff, and you can buy them and cover them with either really cool wrapping paper or fabric and hang them on your wall...or you could buy a canvas and paints and paint (you don't have to be an artist to make art...and it doesn't have to be perfect. imperfections make things special and unique =D)...
Learn to knit or crochett...or they have something called a latch hook kit...and you can make like little rugs and stuff.
when I'm occupied I generally tend to feel better.
I've ALWAYS wanted to make one of these...
http://familycrafts.about.com/cs/sch.../081402a_2.htm
OR you could always cook something. I know that's not as fun when you're on a diet...but if you know someone who you think maybe THEY need cheering up, bake them some cookies or brownies (if you can still resist them that is...lol) and take them to them.
Also, something that generally makes me feel really good is when I completely clean and then re-arrange my room. It's like a whole new space just for me =D