Bankers usually review resumes quickly, so your document must make its strongest evidence easy to find. The goal is not to describe everything you have done. It is to present a focused argument that you have the academic foundation, relevant experience, attention to detail, and motivation needed for investment banking.
For students and recent graduates, evidence can come from internships, part-time jobs, student organizations, athletics, academic projects, research, or entrepreneurial work. Prior banking experience helps, but it is not required for every role. A candidate who has never worked at a bank can still demonstrate financial interest, analytical ability, leadership, teamwork, and comfort with demanding responsibilities.