How long of a ride are you talking about, 20 miles, 50, 100? How many hours of cycling? If you are only eating a single sandwhich < 500 calories, and you are riding more than two hours, then I can understand this.
As a long distance rider with seven - eight years experience, I do NOT eat anything within three hours of a long event (more than 50 miles). I just start drinking when I start pedalling. I say drinking because liquid calories can be more easily digested and pass through your system and become usable energy quicker, depending on the kind of calories you ingest. Take a look at Hammer Nutrition's website and look at their knowledge base for very good, real scientific and real world information.