Right now I'm working my way through an computer science book. Apparently computers will do tasks that I think are boring if I know how to ask them. I really feel like someone should have told me this before. Seriously though, turns out knowing a bit of programming really helps when analyzing fMRI data and designing psychology experiments.
I'm also working through a refresher book on single variable calculus. This one has much less practical importance to my day to day work, but I'm tired of looking at complex computational models of behavior and only barely comprehending the math involved. Even if I get nothing out of this, doing math at 2am should help me get some sleep.
Of course, I also use a lot of this time to procrastinate and read comic books. Last night, I got through two chapters of programming, one chapter of calculus, and six issues of Batman and Robin.