The morning of a half marathon, aim to eat a full meal 2-4 hours before the race. The breakfast should include 50-100g of carbohydrates with some protein and fat. Pre-race fueling is important to top off glycogen stores and provide readily-available fuel for muscles during the race 
A few examples of pre-race breakfast include:
Oatmeal topped with banana, berries and nut butter
Whole grain toast topped with peanut butter, banana and honey
Hydrating before the race is also crucial for your success. The recommended fluid intake varies from person-to-person, but a good rule of thumb is to aim for 2 cups of fluid 2-3 hours before you run, and another cup of fluid 15-30 minutes before you leave for the race. Assess your urine color to see if you’re properly hydrated. Urine lemonade or lighter usually indicates optimal hydration status, while dark yellow means you need to drink more.
You may also want to consider two ergogenic aids on race day-- caffeine and beet juice. Caffeine has been shown to boost speed and performance. Consume 3-9 mg caffeine/kg, 30 - 90 minutes before a race for a total of no more than 400-500mg caffeine per day (roughly 4-5 cups of coffee) [2
Beet juice contains nitrates, which may increase oxygen uptake and improve running performance. The recommended dose of nitrates is 300-600mg (or 0.1mmol/kg of body weight), 2-3 hours before a race [3
]. One cup of beetroot juice contains about 250mg of nitrates.
Lastly, keep the warm up to a minimum. A few dynamic stretches and about 5 minutes of brisk walking, followed by easy running for the first few miles of the race should be adequate to warm up your muscles if you’re not a front runner.
For more information, check out our ultimate guide to running nutrition here