A coco peat brick is also called a coir brick. It is made from coconut husks leftover from the coconut industry so is 100% organic and a very good use of resources. The husks and dust are dried and squashed into a brick making it very easy to transport. It is used in propagating mixes and potting mixes because it is fantastic at holding moisture.
Buy a coco peat brick from a hardware or garden centre. It’s quite cheap and very light weight.
When you want to use it, put the brick in a bucket and fill it with water. In around 15 minutes, it will become re-hydrated and swell up to fill the bucket. One brick will make around 7 litres of coco peat.