If you plan on doing nothing but having fun for a summer, the summer after your first year is definitely the time to do just that!  There will be a multitude of good reasons why you should be doing something productive the summer after your second year. 
    However, after your first year, things are somewhat in limbo.  You don't yet have enough legal knowledge to be overly helpful to an employer, and you'll be quite correctly saying to yourself, “I can always do an extern/internship the summer after my second year or during the school year my third year.”  This may be your last chance at long term play until you reach retirement age.