In the morning of the sportive, wake up early so that you can have a breakfast 2-3 hours before the ride.
Your carbohydrate stores in the muscle will be full from the carb loading the two days before. Your carbohydrate stores in the liver, however, will be very low when you wake up in the morning. Liver carbohydrate stores are important to maintain your blood glucose. When blood glucose drops during your ride you will start to feel weak, dizzy, nauseous and performance will drop! Running out of energy is usually because your blood glucose has dropped and your muscle carbohydrate stores are running low.
In order to fill your liver glycogen stores you need a breakfast that contains carbohydrate, 100 grams of carbohydrate at least. This is the equivalent of 2 bagels or a large bowl of porridge or a large bowl or cereal, or 4 pancakes or 6 slices of toast with jam.
What to take on the ride
Of course you also need to prepare the food on the ride. Make sure you have two bottle, one with a sports drink (typically these drinks contain 30-40 grams of carbohydrate per bottle when prepared according to instructions and not diluted) and one with plain water.
Then calculate your carbohydrate needs and as a very general rule use 30-60 grams per hour. In reality your needs will vary depending on the level of cyclist you are, the distance you are riding and the time it will take you but 30-60 grams as a guide is a good start