It may be too early in your education to know what you want to do in your career, but I would start looking in to areas where you can specialize. Client/server architecture will always be a skill that looks good. If you want to go this route, look into learning Java Enterprise Edition. UI design is good to know, but with abundance of WYSIWYG editors that are available now, writing UIs is becoming less of a skill. UI design theory is still pertinent even if the coding skills are going the way of the dodo. Some other skills that will come in handy are writing web services, database interaction (with JDBC and JPA, both good to know), and multi-threading. I would also recommend the book Head First Design Patterns to get started on learning how to design software (as opposed to just writing software).
I would agree with what a lot of people have been saying, though. The best thing that you can do is put what you know in to practice. Start out writing a small application for yourself. Write unit tests.Do some code coverage analysis on the code and make sure you are completely covered. You can start with Cobertura. Get to know what APIs are available in JSE. I'm assuming that in an academic environment you are using the latest JSE (6), so I would also look into familiarizing yourself with JSE 1.4. There are some major differences between 1.4 and 5 (and not a whole lot of major differences between 5 and 6), and if you are working on legacy code in the future, it helps to know what differences there are. Write an app in whatever you are used to using, write it again with JSE 1.4. Check out an open source project and debug it. Get code coverage on the project and write tests to cover more lines of code. Most OSS projects would be happy to integrate tests that increase their code coverage. Look through the bugs that have been logged against the project. Pick something small, fix the bug, and submit patches. Get familiar with build systems like Maven 2 or ANT. That should keep you busy until next semester.
You can't have everything... where would you put it? -- Steven Wright