Since carbs are so important to your body’s engine, your pre-workout meal should be relatively high in carbohydrate. A little bit of protein is good, too. It will slow digestion just a little bit – enough to allow the carbs to enter the bloodstream a little more slowly and steadily. On the other hand, you don’t want to eat a lot of fat right before you head out – it can slow digestion too much and leave you feeling uncomfortably full. And save your high fiber foods for afterwards, too, since they also take a while to work their way through your system.
As far as what specific foods you eat – there are no hard and fast rules. A Formula 1 Sport Shake works well if you’ll be working out relatively soon after eating; a turkey sandwich and a bowl of soup at lunch will be pretty well digested if you’re going for a run in the mid-afternoon.