What Should I Fill My Raised Garden Bed With?

Hello, I'm looking to start a vegetable garden soon and I've already built my garden bed. I live in the desert and my yard has absolutely nothing but sandy dirt in it, so I was wondering what do I fill my garden bed w/since there are no sticks, leaves, etc? I'm a complete beginner, so sorry if this is a silly question. I saw that compost and topsoil are absolutely mandatory but was wondering if I could just get away with those or if there's something else I can add since I don't have access to other organic materials. Will mulch work?