Why do you think an internship would help as opposed to just getting a job? There aren't any in particular that would be an advantage to an application to the mliitary.
What extracurriculars and hobbies have you had/do you have? You can gain relevant skills from volunteering, mentoring (especially uniformed organisations like Scout/Cadets), involvement in sports, organising events, positions on committees, and these can be done alongside work.