While attending college, what is recommended for college students to do outside of school?
It sounds like you are definitely thinking with a view toward the future. There are several options to consider while you are in College which will demonstrate your leadership ability, initiative, community spirit and/or assist you in deciding if the career path you are on is right for you. You mention internships which are great in assisting with getting your foot in the door in your chosen career. There are recruiters from many industries that will either visit the campus or provide contact information to the various department heads so they can screen prospective interns and/or candidates. Take advantage of those opportunities and get to know your councilors and department heads. If you find an internship that sounds appealing, go for it. Even if you don't get it, you gain from having tried.
Every time you go thru an interview, you gain experience and they become more comfortable so use this time to get familiar with the process. Remember that an interview is a two way street and you are evaluating the company/position at the same time that they are evaluating you. Use that time to ask questions and find out more than "how much does it pay?" Use your time during the school year to participate in extra-curricular activities. Your resume will benefit in that you can demonstrate your leadership capabilities by describing what you accomplished by being engaged.
Community service is another opportunity to demonstrate your willingness not only to learn, but to give back. Remember, you are building your resume which is your story. What you have to say in your story depends on how much material you have to work with so do the things which make you happy and also provides data to show what type of individual you really are. Recruiters and hiring managers are used to seeing resumes for recent graduates who have little to no actual work experience so you must differentiate yourself and give them facts and examples of how you utilize your abilities in areas other than a work environment. Good luck!