No, you can take these trains at no extra charge. In the tourist seasons, it is recommended that you pay to make a seat reservation on these lines, especially at certain times of the day (e.g., the train leaving Montreux at about 9:30am is particularly busy). In addition, they do run special trips on these lines that include gourmet meals, etc. However, to take the regular trains and at this time of year there is no need to have anything more than a normal ticket.