Fueling with carbs during longer runs and races will prevent you from running out of energy and help boost your performance. But what you eat while running depends on your own preferences. Many runners like to fuel with energy gels or chews because they're easy to carry and digest. A general rule of thumb is to take in about 100 calories after an hour of running, and then another 100 calories every 40-45 minutes after that. Many sports gels contain 100 calories, so it's easy to keep track how many calories you're consuming.
Here are some of the more popular energy gels and chews used by long distance runners:

Photo courtesy of PriceGrabberGU Energy Gels are a favorite among marathon runners because they're quickly and efficiently absorbed by your body. Some flavors include vanilla bean, chocolate outrage, orange burst, strawberry banana and just plain.

Photo courtesy of PriceGrabberClif Shot Bloks are a great way to replenish the carbs and electrolytes your body needs. They're very portable, soft and easy to chew, much like gummy candy. Some runners who don't like the taste or consistency of gels prefer Shot Bloks. They come in a variety of flavors, including: black cherry, cola, cran Razz, lemon lime, orange and strawberry.

Photo courtesy of PriceGrabberThe small, easily portable Hammer Energy Gel packs are great if you want to enhance performance and prolong energy levels. These gels are easily digested and uniquely formulated to contain only a trace of sugar, so you won’t experience sugar highs or crashes. Some flavors include apple-cinnamon, banana, chocolate, orange, raspberry, tropical and vanilla.

Photo courtesy of PriceGrabberJelly Belly Sport Beans are a tasty and convenient option for eating on the run. Available in six different flavors, sport beans contain carbs for energy, electrolytes to replace those that you're losing through sweat, and vitamins B and C. They taste very much like regular Jelly Belly jelly beans, but they're just a little saltier. Runners who don't like the taste or consistency of sports gels find these sports beans to be a great alternative.

Photo courtesy of PriceGrabberThese PowerBar Gel Blasts are bite-sized chews that contain a liquid center which will help give you energy during long runs. The gel blasts are formulated with PowerBar's C2 MAX-optimized carb blend which is specifically designed to boost energy in muscles where calories are burned quickly and efficiently. PowerBar Gel Blasts are available in natural lemon and cola flavors.

Photo courtesy of PriceGrabberCarb BOOM! energy gels are made from super concentrated complex carbohydrates and flavored with real fruit purees and concentrates. Formulated with a special blend of 22-25g of complex carbohydrates and just 2-4g of simple sugars, Carb BOOM! gels provide fast and steady release of energy into the muscles. Its rich complex carbohydrate formula is easily absorbed and digested without any stomach upset. Flavors include apple cinnamon, strawberry kiwi, vanilla orange, double espresso, and banana peach.

Photo courtesy of PriceGrabberHoney Stinger Organic Energy Chews are great for althetes who are looking for natural, organic choices for their long runs. These energy chews are unique because they include naturally occurring fiber and protein. The chews come in three flavors: cherry blossom, pomegranate passion and a fruit smoothie variety package.

Photo courtesy of PriceGrabberPowerBar Power Gels come in a convenient 100 calorie pack, which is easy to open and eat during your runs. The gels contain both carbs and sodium, which need to be replaced during your long runs and races. Power Gels come in a variety of flavors, including: chocolate, vanilla, raspberry cream, double latte, and green apple. Some flavors also contain caffeine.