Been fighting over the single USB charging cable in your car? This deal will alleviate all your car-charging-related problems. Amazon has a PowerGen Dual-USB charger for only $7.99, and it's rated at 4.6 stars.
This charger outputs 3.1A across the two USB plugs, which is enough to supply power to two thirsty devices at once. One of the ports is supposed to be for Apple devices, and the other for non-Apple. You should be able to plug Android things into both, but the Apple port might supply somewhat less power depending on the device. Maybe stick your tablets on the non-Apple port just to be safe.
The white version of the PowerGen is the one on sale, but the black is only $9.99 if you're going for some kind of matching scheme in your car. Remember, free shipping is for Prime members, but slower Super Saver shipping is free to anyone else that spends $25 or more.
Note: Prime members can actually get this shipped free overnight until 4PM PT, which is pretty cool.