You could include stuff like:
1) Some relevant courses (from your coursework of last attended college/school)
2) Soft skills that you possess
3) Any (academic) projects that you completed as part of your coursework (or on your own)
4) Any competitions where you won award/prize
5) Any professional memberships that you might have
Hope this helps!!!
Also, a strong resume isn’t the only way you can get your foot in the door for a job or internship. Consider whether you know anyone who might be able to help you out- parents, teachers, friends’ parents, other adults in your community- may work at places that are hiring for the summer. Make sure people around you know you’re looking for a job and will work hard, and they may be able to offer you advice or even recommend you for jobs they know about.