There is a very simple rule to be followed if you're planning on heading from Bangkok to Surat Thani or Chumphon by bus. DO NOT and we repeat DO NOT, take one of the private buses that can be organised from Khao San Road as theft on these buses is endemic. Spend the extra money, go out to Sai Tai Mai (the southern bus terminal) and get a ticket on a public bus down to either destination. We are not kidding when we say theft is a major problem on the private buses -- generally a thief gets in the luggage section with your bags and goes through them during the trip, alighting with all your goodies before reaching Chumphon. If you insist on catching one of these buses do not leave anything more valuable than a bag of soiled underwear in your pack.