If race day temperatures will be hot, with high humidity, and you typically sweat heavily, you should hydrate with sports drinks that contain electrolytes during the event. If you normally avoid eating salty processed foods and snack foods, you could add some salt temporarily ahead of race day. You don't need large amounts of sodium. If you drink water during the race, but don't replace the lost sodium, hyponatremia, or low blood sodium, can be the unwelcome result.