I don't think students should be able to leave their belongings at a computer and go off to lunch or where ever for hours. While they are away someone else could be using the computer. If they have to go to lunch or a class or to have coffee with a friend they should take their belongings with them and let someone else use the computer. if they are going to the toilet or to get a printout okay, but if they are going away from the computer for more than a few minutes they should not be able to hold the computer by leaving their belongings at the computer.