These coaches are usually fully sold, and everyone is bringing their own 20kg with tents and sleeping bags etc etc. If everyone brought crates of beer than it just wouldn't fit. Don't take advantage of the kindness of other passengers who choose not to bring crates onboard out of consideration for the luggage needs of everyone. If you must, then hang back to the end and make sure there's room for the real essentials for everyone before very big quantities of your beer goes on.