The kit you need will depend on which headunit you end up with
In a nutshell, it'll be a quadlock (ie, the connector already in the car) to ISO / JVC / ALPINE / Pioneer etc etc, ie, which ever suits the headunit you decide to buy....
An antenna adapter usually comes with the kit, but again, you may need to buy a seperate one.
If the headunit supports steering wheel controls, you'll also need the correct CANBUS adapter kit for your car too
Usually when you buy a complete kit from somehwere like Connects2 you specify the car it's for, and the manufacturer of your headunit and you get all of the right bits to connect it all together