In general, if you are craving crap you are likely to be deficient in some area of nutrition. Eating enough greens will solve this problem.

Most smoothie bars are serving up so much sugar you may as well be at a Dairy Queen. There are tons of green smoothie recipes online and in books like Green for Life by Victoria Boutenko to help you keep it fresh in the kitch. Get your green smoothie in often and feel the difference.

Here’s one from the article:
Ghetto Green Smoothie
• Fresh spinach
• Bananas
• Water

Fill your blender up ¾ full with the fresh spinach. Add two bananas and just enough water to get it to blend down (the idea is to get as much greens in while maintaining your taste preference). Blend and taste. Too sweet? Add more greens. Too swampy? Add more bananas. You can also add ice or use frozen bananas for a frostier blend.

More nutritional goodness at the site.