I agree with Jamoldo.....
AC 1st class will be a great way to experience real India, real people, real food etc minus the discomfort of other classes. These higher classes generally have 2-4 attendants / compartments (car) to take care of the needs of passengers. They get nice tips and so they take good care of you. Common passengers are not allowed in AC 1st class and at night the doors of the compartment are bolted from inside to keep unwanted people away.

Indian trains always had theft problems (due to large volume) so the locks are designed to be foolproof. There is no way some one can open it from outside using magnet etc. Just be a little careful, keep your expensive stuff (Camera, watch, money, credit card, a good pair of shoes) with you all the time and you should be fine.