WiFi Receiver
Power Supply
Amplifier
5V Converter
Not included above are a pair of 1kOhm 1/4 watt resistors, a single 4.7uF non-polar electrolytic cap, and a scrap piece of aluminum that I think I pulled from a powered sub years ago.
That is a stereo amp, does not have wifi or bluetooth capability, and does not include a power supply.
edit: This is the amp I used in this build: https://www.amazon.com/gp/product/B01M0VZ4SA/ref=ppx_yo_dt_b_asin_title_o03_s00
It was $12.99
I used this: https://www.amazon.com/gp/product/B01M0VZ4SA/ref=ppx_yo_dt_b_asin_title_o03_s00 in this build. You are forgetting about the wifi and the power supply!