I believe in cardio on an empty stomach, but not weight training. If you can, get some oatmeal or bran flakes in you, these are simple to prepare and will make your workouts more energetic. As far as sipping a shake during your workout, it all depends on how long you workout, the typical workout is between 45 minutes and 1 hour, I say get in do what you've got to do and get out, then worry about a shake post workout. If you workout for a long time for whatever reason, be careful in taking in a lot of simple sugar, although your body will use most of it to replenish its glycogen stores, too much will be left to store on the ol adipose tissue. So a during workout shake should consist of a whey protein with moderate carbs, a carb blend would due very well in this situation.