When do students usually buy their textbooks?
Most UC Davis students wait until the first day of lecture to see what exact materials will be required for the class. This is a common strategy, since textbooks are typically not used on the first day of class.
Most students will receive a syllabus prior to the first lecture, which will state what the required textbooks and materials are for the class. However, the syllabus that is provided before the quarter starts is subject to change, and the professor may change the required textbooks and/or not require one at all.