Applying for an internship for the summer is a great opportunity to gain some job experience. However, when filling out your CV many companies look for any type of work experience. Furthermore, they look for people who have volunteered for different charities or organization.
You will need to put down your educational experiences in your CV along with all types of related jobs that you've worked. Even if you've done a job as a cashier, this gives you experience with working for the public and helps to build your customer relational skills. This can be very important to the company that you're applying for.