Fruits, nuts, granola bars, cereal bars, etc...
Just about any portable food source is good as long as you can digest it while riding and it has a decent quantity of carbohydrates. Sugar in and of itself is not bad, as long as it is consumed in moderation. Fresh fruit, I like apples and bananas on the bike.
Like wog said water is important. You need to consume enough during the ride that you don't feel thirsty. A drink every five to ten minutes seems to work for me, but your mileage will vary...