1. Catching up with people
Odds are, there's someone whom you haven't seen in a long time. Why not take the opportunity to go over the time you've been apart. Especially if you or they live somewhere far away.
2. Planning a schedule for the upcoming term
So you might have messed something up last quarter. Maybe your grades weren't as high as you wanted. Maybe you didn't get into some kind of programme, maybe you got really tired or stressed. Well, it's time to make a plan to prevent such a situation from arising next quarter.
3. Make a schedule for the break and stick to it
Planning out your days will keep you occupied and productive, stopping you from getting bored. Keeping a regular schedule is actually a healthy habit, especially when it comes to when you eat and sleep.
4. Study for your next classes
Sure, it's break. School is over and shouldn't be an issue at the moment. Keep in mind that you can use this time to get ahead in your classes. Does that physics class look scary? Study for it now, and you might get an A. Does that art class look relatively easy? Study for it and make sure you get nothing less than an A+. Kill it on studying over break, and you'll probably kill it in class.
5. Take an online class
If you so wish, you can take online classes and attempt transferring credit to your university. Make sure your university accepts credit for that class if getting required classes out of the way is your primary intention.
6. Acquire a new skill
Did you want to learn to play the piano? Did you want to start speaking Korean? Get started over the break. There are so many resources available for free. Take advantage of them, and go hard while you can.
7. Go on a book binge
Reading is arguably the best pastime for your brain. It doesn't have to be a very difficult book, but at least read something to keep your mind sharp for the upcoming term. Better yet, finish the required reading for your upcoming classes over the break. It might give you a lot more time to breathe during the term.
8. Work on your CV
You might be applying for certain positions here and there, and you'll have to show them a CV or a portfolio. Take this down time as an opportunity to brush it all up, and pay attention to detail. Adding in the smallest item could be a dealmaker or dealbreaker.
9. Fill some applications
Scholarships, grants, jobs, internships, anything. Take some time to fill them out. The further way the deadline, the better. Early applicants are typically seen as more determined to get their foot in the door.
Physical health is just as important as mental health. Take care of your body by moving around a little bit. Try to beat your 5k time, make an attempt to do an extra set of pull-ups, increase your stretching range, or practise that martial arts form you never finished. It doesn't matter. Just try to stay active for an hour or two a day.