Drinks, bars, gel prodcuts, candy (yeah I sometimes carry some in my pocket) all will help with energy - glycogen - levels.
I just bought Hammer Gel. It came in an economic bottle with 26 servings, for around $18. That's about as cheap you'll find. It contains long-chain starch molecules, which essentially supplies more sustained blood glucose, without a 'sugar' crash. Now I only wish I did not buy the 'Unflavored' stuff. I tried it on my first ride yesterday using a small plastic flask in my jersey pocket. I found it very easy to consume and felt very energized -- the whole time.
Prior to this I had been eating Power Bars. Not too much protein. Protein causes blood flow to be directed to the gut, for aid in digestion. We want the blood in our legs. They also have a ~50/50 breakup of sugars and starches, gramwise. It is tested and proven that fructose sugar molecules, in the presence of glucose, synergize and increase the speed of glycogen synthesis. I believe this is because fructose is steadily uptaken in the liver, while glucose goes to muscles rapidly. In glycolysis glucose can enter the cycle immediately, while fructose has to be changed first. BTW sucrose (table sugar) is a mixture of fructose and glucose, near 50/50.
On the topic of glycogen, there is caffeine. Caffeine in the presence of carbohydrates increases the creation of glycogen. I only bring this up because you mention your concentration was waning during strenuous riding. Caffeine would help with the mental focus, and it also lowers your levels of perceived exertion. I find it lowers my tolerance threshold for the lactic burn. I dunno, just an idea.
I am neither a power bar nor hammer gel employee.
Hope this helps.
oops, my suggestions are for rides greater than 3 hours.
