Mattel's super small "Stealth Rides" aren't making their official debut until the Toy Fair later this month, but for all you know the guy next to you could be packing one... right... now.
They're about the size of a credit card and the width of a cellphone, and with the push of a button they unfold into a remote control car. Apparently the Stealth Riders will come in five models: a "Batmobile Tumbler," and four others that I immediately forgot about once I heard "Batmobile Tumbler."
How it works: the folded up cards fit into a small case that also functions as the remote control. Just slide the car out, pop it open, and go to town for up to a half an hour. Or however long it actually lasts in real use.