Well think of it this way....would you attempt to drive you car on empty or almost empty?? Risk putting stress on the engine and embarrassingly breaking down in the middle of the road having to fork over the dough for a tow...not so much!
Well think of your body the same way. Your body works so much more efficiently, just like a car, when it is properly fueled. That pre-workout snack gives you the energy to really push thru that workout, making the most of your time, rather than just dragging through each exercise.
You want to aim for a 100-200 calorie snack that is easily digested. Try to aim for foods lower in fiber and quick in gastric emptying a good 30 minutes prior to your sweat sess. Search for easily digested foods so that your body has already digested them when it comes workout time; those workout tummy aches result when the body is still in the digestion process and you start pushing it to get active.
The best pre-workout snacks are higher on the carb side and about 25% protein. Think a piece of whole wheat toast and almond or peanut butter, a small apple and half a string cheese, single serving Greek yogurt, apple and nut butter, half whole grain bagel and jam, cereal with reduced fat milk or almond milk, a banana, Kashi bar.... Find the best snack for you. Everyone's body works differently.
And no worries if you are serious about your workout you will burn thru this in the early stages of the workout.
Remember to fuel that engine. You only get one! Take care of it.