It's always important to stay properly hydrated, but even more so in the summer. Higher temperatures and humidity make it critical to stay hydrated with proper fluids throughout the day, and especially while exercising outdoors.
I personally start my day with my mocha protein shake and one of my David Kirsch One of Kind® concoctions -- a mixture of energy bubbles, vitamin/mineral super juice and muscle restore -- mixed in super-hydrating coconut water. Then I follow up with iced green tea (instead of coffee, which can be dehydrating).
While carbonated sodas and sugary juices may seem to give you a quick burst of energy, in reality they can lead to a seriously damaging crash-and-burn feeling by mid-day.
Don't forget that whole fruits are excellent sources of water, too! Some of the most refreshing natural snacks also replenish your body with the nutrients and water that it needs, so dive into watermelon, apples, peaches or berries!