For a natural energy-boosting alternative to caffeine, try a small all-fruit smoothie when you hit your mid afternoon slump. The simple sugars in the fruits will provide you with an immediate source of energy to get you through the afternoon. For an added bonus, add a shot of wheatgrass. This superfood is full of antioxidants and stimulates the metabolism. You can get a shot at your local health food store or juice bar for a few dollars, or purchase the supplement in powder or pill form.