You have enough stored glycogen for about an hour's workout and after that, you're right, you need something more. Rule of thumb is your body can only absorb about 250 - 300 calories an hour, so you want to try something in that range (spaced out - not just 300 calories bang! on the hour), with an emphasis on carbohydrates.

Here are some examples of 250 calorie great on bike fuel from a handout I prepared for my TNT Death Ride team:

What does 250 Calories look like:

• bagel - 1 ½
• Peanut butter sandwich - 1 small
• Turkey sandwich (no mayo) - 1
• pretzels - 45 small twist pretzels
• bananas - 2 - 3 each
• oatmeal cookie - 2 - 3 large
• chili - 3/4 cup
• Coke or Pepsi - 1 ½ cans
• Fig bars - 5 each
• boiled potato - 2 1/2
• Potato chips - 25
• Clif bar - 1 each
• Luna bar - 1 ½ each
• Clif blocks - 7 - 8 each
• Payday bar - 1 bar
• Hammer or Power Gel - 2 ½ servings
• Gatorade (original or endurance) - 40 ounces (!)
• Powerbar Performance drink - 30 ounces
• Jelly Belly Sport Beans - 2 ½ packages

Complex, long-chain, sugars are best. Avoid simple sugars. Not only are they calorically dilute, but it is like trying to fuel a fire with newspaper instead of wood - it burns quickly but you have to keep feeding the fire.

ETA - don't forget liquids and electrolyes. (That's a whole other handout. Yes, I am a geek, but it really helps my coaching to get organized and do these handouts before my clinics.)