Becoming paranoid is not the way to avoid becoming the victim of theft. But by preventing the opportunity for a thief to prey on you, the risk is significantly reduced. Keep your real valuables with you at all times. It could be rifled through in seconds by the person sitting behind you. Place it on the floor with one strap looped under your chair leg.
Staff have keys too.
Backpacking with expensive watches and CD players will only make you more paranoid about being robbed. They may snatch your bag just as the vehicle is pulling away, leaving you helpless to get it back. Keep some money in your front pocket to use. Use a washroom or other private area if you must access your money belt. It only takes a thief two seconds to grab your backpack and disappear into the crowd.