It's very important to eat during a long ride because you will be burning calories and your
body needs that energy to continue riding.
A very simple rule of thumb (which can vary from person to person) is to consume approx. 250 calories per hour of riding. As an example, a PowerBar Performance Energy bar is 240 calories. So that equals approx. 1 bar every hour of riding. Typically an hour of riding is every 15-20 miles (depending on your mph average). So that's makes it really simple, eat a bar every break and you should be all set.
Other people prefer to put those carbs and calories in their drink mix and drink throughout the ride.
Others' prefer the natural method: fruit (bananas, apples, oranges) peanut butter and jelly sandwiches.
And other's prefer to mix all of the above.
Bottom line, find what works best for you and don't forget to eat throughout the ride!!