Keeping hydrated while riding is crucial when riding, most commonly used by mountain bikers, Hydration backpacks have a removable bladder secured in the pack with a hose guided out the top and clipped to the strap. The hose end has a unique bite valve to drink from. Easier than stopping to grab the water bottle in the frame and the bladder can carry more. Camelbak and Evoc lead the backpack game here but you can also find great options from Scott and Thule.