I've been using caffeine on Tuesdays and Thursdays to get me through my first couple classes. I am taking an energy drink during the first class. I don't think it's a good idea to continue relying on drugs to get you through, but I figure that it can't be too bad for me to shock my system twice a week as long as I don't keep it up indefinitely.
I don't drink it if I'm functional enough to not need it. This usually happens on nights after I get a lot of sleep. I think that sleep is way better than caffeine for producing an alert mind and responsive body. It's just that sleep's a lot harder to get than paying a couple $$$ for a stimulant.
I've tried a few different energy drinks and my favorite is by far Rockstar's Guava flavor. It comes in a purple can. You should try it if you're so inclined.