A flipped classroom, an approach abandoning traditional lectures and having students come together to apply acquired knowledge, requires students to come to class well prepared. The nature of this preparation is currently being debated. Watching web lectures as a preparation has typically been recommended, but more recently, a variety of study materials has been considered to serve students personal learning preferences. The aim of this study was to explore in two flipped courses which online study materials stimulate students most to prepare for in-class activities, to find out whether students differ in their use of study materials, and to explore how students use of online study materials relates to their learning strategies. In a basic science and a clinical course, medical students were provided with web lectures, text selections, scientific papers, books, and formative test questions or case studies. Use of these online materials was determined with questionnaires. All students watched web lectures and read text selections to prepare for in-class activities, but students differed in the extent to which they used more challenging materials. Additionally, the use of online study materials was related to students' learning strategies that involved regulation and monitoring of study effort. Our findings suggest that students have similar learning preferences as they all use the same "basic materials" to prepare for in-class activities. We interpret the preferential use of web lectures and text selections as being regarded as sufficient for active in-class participation. The less intensive use of other study materials may reflect students' perception of limited study time.