Signing up for an internship at a company you'd be interested in working for after graduation would be ideal. Some of the larger corporations offer paid summer internships. It's not uncommon for students to graduate knowing they have a job waiting for them.
However if you can't get a job at your ideal company then working for another type of company will give you an edge over someone who has simply been a "full-time student" all of their life.
You also have an opportunity to network as well as get some professional references. Job hunting has become extremely competitive. Having a degree alone is not going to part the red sea.