leaving electronics in your car is a bad idea. it is bad for your electronics to be in extreme conditions. different electronics have different tolerances to hot and cold and say it on their packaging or booklets somewhere. but the cold can freeze the internal components and then they could break. the heat can cause batteries to explode or catch on fire. Cold conditions can also freeze the plasma in the lcd screens which will cause them to lave th image still on the screen for some time. if it happens every now and then ur probably ok. but it is best not to make a habit of it. cd's are probably ok