Amp, wiring harness, sub and enclosure. The overhead slider is optional, I chose not to install it because I didn't want to take my A-Pillar off and possibly break it.
It's a wiring harness that connects between the head unit and the car's radio plug, and it also has a connector for the amp, (possibly a connector for the overhead slider), and lastly a connector for the sub. The amp is located behind the carpet on the passenger side in the center console, down by the floor. You can post a for sale thread in the mall asking for a harness, there's many people with extras. I got mine for $25.
The previous picture shows the radio, amplifier and subwoofer harness. Here's the one showing the subwoofer wiring routing to the overhead light switch.