Which of the following is NOT part of the critical items to check when you stop?

When conducting a pre-trip inspection, it's crucial to focus on items directly related to the vehicle's immediate safety and operational performance. The correct choice is engine oil level because, while it is important for the overall health of the vehicle and should be checked regularly, it does not represent an immediate safety concern when you stop the vehicle.

Brakes are essential for controlling the vehicle and are critical for preventing accidents. Lights and reflectors are vital for visibility and communication with other drivers, especially in low-light conditions. Operating trailer coupling devices ensures that the trailer is securely attached, preventing detachment while driving. In contrast, checking the engine oil level is not categorized as an immediate concern during a stop, making it the correct answer for what is not part of the critical items to check in that context.