It's a total cliché, but you already know the answer. Work out, eat better (not just quality of the food, but make sure you're eating enough) and try to figure out your sleep patterns. If you feel like crashing in the afternoon take a short nap (shorter than 30 minutes), or if you have the time, you can go for a full sleep cycle (about 90 minutes). Also, if you're depending so much on caffeine make sure you drink enough water...caffeine dehydrates you quite a bit. Add all that crap in an energy drink and the effect's worse. When I'm cramming I usually have a glass of water per cup of coffee, and I'm constantly sipping water anyways. Sometimes when I'm super tired I'll pop down and do some push ups or run up and down the stairs and that'll kick me back up.