What's your favorite inter-car communication system?

If you're going on a drive with other people in other cars, what do you use to talk to them - especially in the absence of reliable cell service?Walkie-talkies? CB radio? HAM radio? Semaphore flag signals? Middle fingers? If you use a product, what's your favorite? What kind of range do you get? via /r/cars http://ift.tt/2s4jCWt