Fast digesting carbohydrates are useful to make sure your body has fuel through all 26.2 miles. A fire extinguisher is neither useful or not useful. A weight vest is not useful if you’re attempting to run your personal best. The extra weight will slow you down. Scissors are dangerous, you should never run with scissors. Running shoes are very useful to project your feet and enhance your biomechanics and the efficiency of your stride to run your best time.