While textbooks serve as a primary source of content material and problem-solving practice for undergraduates in engineering, studies that investigate how engineering students prepare assignments based on textbook problems are limited. To examine how engineering students complete textbook-based assignments outside of class, this exploratory qualitative study retrospectively investigated the study behaviours of six undergraduates enrolled in a required, second-year undergraduate engineering course at a mid-size, public university in the western United States. Within the course, students solved textbook problems and electronically submitted problem answers for graded credit. Findings from in-depth, semi-structured interviews showed that students identified and used a variety of non-traditional and unsupported resources in personalised approaches to preparing assignments. Resource choice and use was affected by students' preferences for timely support, convenience, and social connections. The online submission process seemed to influence students' adoption of study behaviours and resources considered less effective for deep, conceptual learning.