12. Not Taking Advantage of the Library
You know what the library is full of? A lot of free stuff. Free computer time, free resources, free presentation rooms, peace and quiet; there are a multitude of things available in the library at no cost to you. Technically, your student fees fund all of that, so in reality, if you're not visiting the library, you're throwing your money away. Do you really have cash like that?
Though it's a prime location for studying, it is also good for naps. Have a one hour break in between classes and don't know what to do? Catch some z's in the astronomy section; no one is ever up there.