Well, the Cherry Pepsi (assuming it's full calorie) will have about 150 calories in a 12 oz can. That's a lot of empty calories. It also has caffeine so you'll have to drink a significant amount of water to make up for the diuretic effect that it has. I think the rule of thumb is twice as much water as the caffeinated drink (if you drink 12 oz of pepsi, drink 24 oz of water).
Besides a high calorie count it has loads of sugar. Sugar increase the blood sugar level which increases insulin output which returns a fast, sharp decrease in blood glucose into cells which results in feeling hungry, tired, craving more food and the cycle starts all over.
