DON'T BONK
"Bonk is a funny name for a terrible feeling, when suddenly there’s nothing left in the tank, the legs turn to jelly, and getting to the finish or just back home becomes an altogether supreme effort of will."
(bikeradar.com)
Energy Deficit
Cycling, even at a slow or moderate pace is great exercise and with exercise comes the expending of energy. When that energy isn’t replenished, you may end up in a deficit, where every pedal stroke feels laboured, you are excessively tired, and your focus may no longer be where it should be. Food and hydration play an important role in managing your energy requirements and will help prevent Bonking.
Food
To avoid an energy deficit, it is good practice to eat small amounts of food relatively often during a bike ride, especially if you plan on being out for longer than 2 hours, or will be riding at a very high intensity. Foods such as cereal bars, bananas, energy bars, candies, rice cakes, pastries or sport specific foods, like energy chews and gels, are good choices to consume while riding. Each rider will need to experiment to determine what foods work best for their riding style and what their stomach can handle.
Hydration
It is also very important to stay hydrated on the bike, even in the winter months. A general rule of thumb is to consume one water bottle worth of water, electrolyte mix or sports drink every hour and to drink a little at a time and often. Don't wait until you are thirsty to start drinking. Various factors, such as level of exertion, temperature and wind, may require you to drink more or less liquid.
There is a lot of information on cycling nutrition and hydration on the internet. For a thorough assessment of your dietary needs, consult a nutritionist or doctor.