Try something new and STICK AT IT for the year- no matter how rubbish you think you are at the start, seeing yourself improve at it over the year is so satisfying.
Make friends with people from different cultures- when are you going to get the opportunity again to meet so many people from so many backgrounds? Learn about their cultures, ask them to cook you a signature dish etc.
Pursue your hobbies to the maximum. Course dependent, but in general you are never going to have this much free time again, When else would you get 4 months off for the summer? And have nowhere to be at 11am on a Tuesday? Use the spare time productively- enjoy your hobbies and passions while you still have the time to.
Read as much as possible. Find out what you love/ don't love about your discipline. Find out what you love about other disciplines. Use your university library to your advantage, see it as an opportunity to gain knowledge, not a place you dread going to.