This study probes the influence of smartphone usage, backpack positioning, and varying neck angles on muscle activation, postural sway, and body discomfort during simulated public transportation. The experiment included 10 participants, aged mid-20 s to mid-30 s, with parameters including distinct neck angles and backpack positions (no backpack, front, and back). Findings reveal that the front backpack position generally caused the most significant postural sway and highest muscle activation, notably for the gastrocnemius (GN) muscle group and the overall muscle group statistic. Body discomfort surveys further indicated increased discomfort with the front backpack position, especially at a 45° neck angle. This research underscores the ergonomic implications of smartphone usage and backpack carriage during public transportation, which can guide future public health interventions and transit design strategies.