Google Camino Packing Lists and look over a bunch to see common items and suggested brands which will vary by gender/location/age/personal preference. Some will have links to Amazon for gear to give you an idea of prices if there are things you will need to purchase (scroll down the Amazon page for package weights if its there).
In short you will need clothes, shoes and a pack. Rain gear. Warm gear. Cool gear. Toiletries. Water bottle. Electronics and chargers. Sleeping bag/blanket.
Start with what you have. Think about what you usually pack for a holiday. Make a list of the things you think you will need, stuff it all in a pack to find out how much it weighs and then start pulling out the things you won't need - if something is needed on Camino you can find it in one of the cities.
Buen Camino!