Solution: After running, especially a long run, you want to replenish energy as quickly as possible. Studies have shown that muscles are most receptive to rebuilding glycogen (stored glucose) stores within the first 30 minutes after exercise. If you eat soon after your workout, you can minimize muscle stiffness and soreness.
You'll want to consume primarily carbs, but don't ignore protein. A good rule of thumb for post-run food is a ratio of 1 gram of protein to 3 grams of carbs. Nutrition bars, such as Clif bars or Power bars, are healthy options. Other examples would be a bagel with peanut butter or a smoothie made with fruit and yogurt.
If you feel like you can't stomach solid food immediately after a run, try drinking some chocolate milk. Chocolate milk provides plenty of protein, carbohydrates and B vitamins -- making it a great recovery drink. And cold chocolate milk tastes pretty refreshing after a run.
Making sure you eat within 30 minutes of finishing your run may require some planning. Try to think ahead and make sure you have recovery foods available when you end your run.