Each 5 gallon compost tea brewer comes with one brew kit to get you started. Additional kits are available.
The Eco-Tea brew kit is optimized for the Overton Eco-Tea brewer. This kit is a more refined version of the basic brew materials. It contains the microbial foods, high-quality compost, and a microbial catalyst in separate pouches. It does not contain a mesh bag, which is part of the brewer.
You can also come up with your own compost tea ingredients, but then you really need to get into testing them to make sure you make a good tea, so for most people, it's better to buy the kits that are proven to work.