So if you want to do what i did and have a new head unit, speakers, subs and an amp for each youll need a few supplies for sure.
Headunit, panasonic, alpine and pioneer all make good ones
Speakers: Inifinity kappa or alpine type Rs anything else is a waste of money IMO
You need two amps on 4 channel for the speakers and one Class d mono block if your running two subs or a 2 channel if your running one. Anywhere from 300 to 1000 watts is plenty for the bass to shake the car. You probably want about 100 watts to each speaker.
You'll need wires and fuses 4 gauge should be ok and at least 150 amp fuse. Most electronics stores will sell an amp wiring kit, let them kno you want two amps and they will adjust it accordingly
For subs MTX are great for a budget the alpine type Rs or type Xs are killer same with the Kappa Perfect series.
You need a bunch more odds and ends but that should get you started.
A complete stereo replacement will run anywhere from 500 to 5000 bucks and should take at least an afternoon depending on how savy you are.
Hope this helps