1) Buy some of your favorite flowers and arrange them in a pretty vase. I like roses, tulips, peonies, and hydrangeas. Something with lots of color, size, and scent. Or I get myself a new huge scented candle, and chill out with it while reading or playing video games.
2) Give yourself a mani/pedi, or get one done if you can spare the money and time. I haven't had a professional one in years, but I'd like to at some point. In the meantime, I invest in some good quality polishes, nail clippers, and polish remover and I clean, trim, and repaint my nails every week.
3) Go have (ONE of... haha) your favorite junky treats...burgers&fries, chicken fingers, a milkshake, or something from Cold Stone always does it for me. If I want a comforting pick me-up at work, I make a run to Starbucks for my favorite coffee treat (tall dry cappuccino with vanilla syrup and cinnamon powder)
4) Clean something... your place, your car, your computer's hard drive. It may not be super fun, but it's definitely productive, which usually makes me feel accomplished, and then better overall.
5) If the problem is related to clothes but you don't want to go shopping, shop your closet. Pull out some things you rediscover, febreeze/iron them, mix and match them with other pieces, and then hang them somewhere you can easily see them (I use a rail over my washing machine). Did this one just yesterday, so now I have a rail full of "new" work and casual outfits that I can't wait to try out.
6) And last, hop online and browse your favorite stores and make a note of the things you'd like to try out during a future shopping trip. Next time, it's all about H&M for me: