FYI most devices that charge via USB cable charge at 5 watts (5V @ 1A). The exception is the Ipad that charges at 10 watts (5v @ 2A).
Converting DC to AC to DC is very inefficient and unnecessary in most cases. Just use a cigarette lighter adapter. There is no need to use an inverter for the devices that you have listed.
Yep! That's true. All the above listed devices usually come with small, DC adapters for charging and operating the device. I just didn't think about that until you mentioned it. (Guess my mind's starting to go--my wife said it was the second thing!