The body kit comes with the body and everything that is integral to it. You get the body, the back block, the asa, the feed tube (standard issue stuff). You also get the LPR, and the ram (both are integrated into the body). You also get the bolt, the valve, the hammer, the velocity adjuster and the springs.
If you buy a kit, you need a trigger frame, a barrel (can be purchased with the body kit at a discounted price), a 3 way, and an inline reg.
Or if you want to get an electro trigger kit (eblade or race frame) you just need that and the inline reg (and barrel of course.