Can anyone tell me what this is? Found it in the cup holder,

 

Perhaps a fuel filler tube? This would allow you to add gasoline by hand using a common gas can, if you ever run out of gas on the road. There is a locking plate on the fuel system that precludes someone sticking a hose in there and stealing your fuel. But that locking plate also stops you from adding fuel when you need to. If so, that tube will be a tight fit to area inside the gas cap.