How can I keep my iPhone / iPods cooler in a hot vehicle?

Solution 1:

Place the electronics that contain a lithium based battery in the shade and keep windows open a crack. If possible, place the vehicle in the shade or use light or reflective colored windshield shades to reduce the heat that stays in the car.

Usually the trunk (or a well insulated bag) will lag the passenger compartment many tens of degrees and warm up several hours slower than something in the main cabin.

Solution 2:

Coffee cups (with lid, of course)

The most flexible and cheap solution are coffee cups. These cups are usually designed to have insulating walls.

Insulation is the most effective way to prevent heat building up. You might want to prefer white cups, but it should not make much of a difference.