How to send things back from UK?

May not be the best place to ask, but this is my first time and I am moving back home to Hong Kong soon and would like to know what's the cheapest way to send my stuff back (i.e. stationeries, clothes, books)? | have done some looking online and it's confusing that there doesn't seem to have an sea freight option. I don't have a car so the best way is to do door-to-door with my parents waiting on the other side of the world. Also, do shipping companies take in any boxes for shipment? I have some cardboard boxes from storage companies for moving flats previously, not sure whether they will accept them. Thanks!