One way to get carbs on the run is through sports drinks. Solid foods can be tolerated, but they need to be small and easy to digest. There are numerous products on the market, such as energy gels, bars, and even sports jelly beans, designed for long-distance runners to eat on the run. Some runners prefer to eat pretzels or sugary candy such as gummy bears or candy corn. Start experimenting with different foods, gels, and bars on your long runs to see what you prefer.
So how much do you need to eat on the run? A basic rule of thumb is that you should be taking in about 100 calories after about an hour of running and then another 100 calories every 40-45 minutes after that. You may need more depending on your size and speed, so make sure you carry an extra one or two gels (or other food). If you feel hungry or low on energy, you can definitely consume calories "off-schedule".