Suggestions for Internship Downtime

Hello fellow WSO users! Long-time reader and first-time poster here.

Started my sophomore summer internship around a week ago at a hedge fund and have found myself with some occasional downtime as I get into the swing of things. Was curious what people have found to be the most productive way of spending their time when things slow down at the office (and yes, I do check in with my boss to see if he needs anything atm).

As I am still new here, I have spent time flipping through some old presentations, catching up on news, flipping through Rosenbaum's book on Investment Banking, and perusing WSO [way too] extensively.

I'm sure this question may apply to many other interns this summer - what is a good way to spend downtime?