What do you get a teenage boy as a Christmas present?

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I've done a lot of Xmas shopping already, but I'm a bit stuck with a teenager, he likes cars, but I haven't seen anything car-y and when I do see things, I think he's probably too old now or not quite old enough, I would just get him smellies but I think he's too young and would still rather have somethinghe can appreciate, any suggestions?