My wife is well trained ... prior to throwing anything plastic away she asks if it can be used for the sons railway.
The latest 'find' was one of those children's novelty battery operated tooth brush's. The batteries can be replaced but the heads cant.
This one had a pair of red flashing lights on a fire engine. Once cut along the glue lines the motor (3 volt) can be removed plus, after removing several small screws, a circuit board containing the lights.
OK it's not to 00 scale but for a children's layout it will be easy to house the circuit board in a rectangular 'box' to form a single set of the warning lights at automatic level crossing. Even with two in series it will only be rated at 6 volts so I will add a street lamp at the crossing or mount a simple battery box under a gate house cottage to power it.