All these energy drinks and bars are just a bunch of crap. All they do is give you a very short burst of energy, that'll eventually leave you more tired than you were. The reason is because most of them contain ****loads of sugar, which the body transforms into glucose, which takes a LOT of energy to do, kicking your body into high gear, which is the famous sugar rush. If you are a sugar fan, it's better to let the bees do the work for you, and use something with honey in it. Honey has already been turned into glucose by the bees, and is very good for you.
If you want energy, make sure you eat stuff with lots of carbs in it. Recommended foods are white rice, pastas, and chicken. Eat this as your meal(s) for the day. As in between snacks you should stick with the tried and tested fruits, bananas being particularly good as they are high on carbs as well.
Keep in mind though that these are not the kind of foods you want to eat when you are trying to loose weight (yes, this includes bananas), but they are great when you are trying to attain muscle growth.
Make sure you stay well hydrated. Don't drink anything with a lot of sugar in it, as this will only make you more thirsty, because of the energy rush your body will put on to make convert the sugars into something useful. It's best to drink what nature has put in you, namely water. Specific sports drinks like Gatorade are useful too, as they will help your body to retain water, and prevent dehydration.
If you feel that you are in need of extra energy, don't give in to the energy bar/drink malarky, instead it is best to apply your own energy reserves. This would be your fat tissue. Yes, that's where your body stores it's extra energy, and that's where you should get your extra energy from. This can be done by using so called fat burners, something which is quite common in professional sports, but be careful when using this stuff, the most powerful work really well, but have something called ephedra (not sure of the spelling) in it, which can be dangerous to the heart if taken in too large a quantity. For this reason most of the fat burners containing ephedra have been banned in a number of countries.
Hope this helped somewhat.