toyota camry hybrid wallet size backup for electronic key

I recently purchased a Toyota Camry Hybrid which has an electronic key. For years I have always carried a spare key in my wallet in case I lose my key or lock it in the car. There is a physical key that comes with my car that will open the doors but will not start the engine. The owners manual indicates that, in case the electronic key dies (e.g., dead battery or other malfunction) you should hold the key with the Toyota logo face down to the start button to start the car. This would seem to indicate that there is some sort of magnetic coding in the key that can be read even if the unit itself does not work. Does anybody make a device like a magnetic card (similar to a credit card) that can be individually coded to start the car in case you lose your key? I have this recurring nightmare that I am camping in Yosemite on Saturday evening, l lose my key and the nearest Toyota dealer is 300 miles away and Monday is a holiday.