(1) Background: trays are surgery-specific sets of required materials and medical devices, assembled in consultation between manufacturer and user, and provided in a sterile package.; (2) Methods: in a high-volume urological center performing 11,920 operations/procedures annually (2023), we prospectively evaluated the effect of trays compared with the standard approach in a comparative study of 64 operations conducted between October 29 and November 30, 2024. The primary endpoints were the amount of operating room (OR) waste (volume/cm³, weight/g) and setup time (minutes). The secondary endpoint was the workflow assessment by nursing staff, rated on a numerical score (0–10) across seven relevant domains.; (3) Results: for endourological procedures, setup time was reduced by 35%, operating room (OR) waste by 34%, and waste volume by 19.0%. Workflow was positively rated with a mean score of 9.75/10. For major open procedures, setup time was reduced by 43%, waste weight by 24.8%, and waste volume by 32%. Workflow was positively rated with a mean score of 8.9/10; (4) Conclusions: Trays have a sustainable and significant impact on reducing OR waste, save nursing staff preparation time, and facilitate improved workflow in the operating room.