amp for sub, amp for highs, component systems, MAYBE rear fill, custom kick panels, head unit, crossovers, equalizers, maybe mobile entertainment, tv's, wires, fuses, alternator, battery, ect....There is so many different things you can get. It depends on how picky you really want. Maybe the average person that doesn't know much about car audio would get cd player, sub and an amp. But most would go up to component speakers, and maybe an equalizer. And then there are those that take the extra step by going into tv's which would mean additional speakers for surround sound and different processors to get the surround sound. It all depends.