If you want to delve into the details, use a search engine and the key word maltodextrin, the most common constituent of all energy bars/drinks/supplements. Maltodextrin is a creamy white hygroscopic powder, moderately sweet in taste, produced by partial hydrolysis of starch. It is a mixture of glucose, maltose, and polysaccharides. Maltodextrin products are assigned a value describing the Dextrose Equivalent. Products with DE-values from 6 to 19 are called Maltodextrins, those with DE-values from 20 to 91 are generally deemed Syrups (the most common is 'corn-syrup' such as Karo). Products with DE-values of 92 to 99 are called 'Total Sugar'. A value of DE-100 is equal to pure Glucose (Dextrose).
Typical Analysis of 100 grams of Maltodextrin powder shows 94 grams of Carbohydrates (with the remainder being residual moisture) containing 368 Calories and 62 mg of sodium. The carbohydrate breakdown is: monosaccharides (glucose) - 4.5%, disaccharides - 4.5%, trisaccharides - 4.5%, and higher polysaccharides - 86.5%.
Commercially, the maltodextrin product that seemed to make the most sense was Hammer Gel. It didn't contain the usual laundry list of additives and the claims seemed reasonable. As noted in an FAQ on their website: The lack of simple or refined sugars, artificial sweeteners, herbs and other bogus ingredients is what makes Hammer Gel stand out from all the rest. We do not believe any of these things enhance optimal performance or health, which is why you won't find them in Hammer Gel. Due to the absence of simple sugars, Hammer Gel requires much less water and is less likely to cause upset stomach or GI distress. It was also one of the least expensive.
A number of wholesalers sell maltodextrins packaged in in 50 poound bags. Commercial products come in smaller amounts (usually 2 to 5 poounds) but the cost per pound is higher. Any of these products can be used to start from scratch to build your own personal supplement (favorite flavor ideas include Tang and Kool Aide crystals) or added to a commercial drink. Personalizing the taste and minimizing the cost per Calorie are generally the reasons you would go to the extra trouble.
Another option is Karo corn syrup. Per the manufacturer, 100 grams will contain 76 grams of carbohydrate and 300 Calories. There will be 2 grams of fructose, 20 grams of glucose, 10 grams of maltose (a disaccharide), 8 grams of trisaccharide, and 36 grams of polysaccharides. (For reference, 2 Tablespoons = 41 grams total weight with 31 grams of carbohydrates and 120 Calories.) The major disadvantage (for some) is the glucose content which can occasionally cause nausea or lead to an insulin surge IF one is not continuously exercising. A Karo syrup based supplement does offer an alternative part way between a pure sugar drink such as Coke and the higher priced commercial maltodextran products. Just buy a refillable plastic tube from a camping or athletic store for packaging and you are limited only by your own creativity.