These calories should be from moderate to low glycemic index foods, and taken 3 to 4 hours prior to the start. You will want to limit the amount of fats and fiber to insure that you do not slow your digestion or risk GI distress. Some great options include Boost, Ensure, "Fuel for Fire" packets, bagel, unsweetened apple sauce with a scoop of whey protein, etc.
You should also continue to sip on sports drink and take a gel approx. 15-30 minutes right up to the start of the race.
*Note: Carbohydrates bind water, so you may feel a bit heavy heading into race morning. This excess water will help to keep you hydrated.