Fictional doodad: Super-smart talking cars like KITT from Knight Rider. The Knight Industries Two Thousand (that number's how you knew it was cutting-edge) not only told David Hasselhoff where to go, it also told him when to go. *Snort* Michael Knight's bulletproof car of justice also sported that famous Turbo Boost too, for making sweet jumps.
Real-world counterpart: SYNC. Most GPS systems will do the whole talking-to-you-so-you-don't-get-lost-or-lonely thing, but the joint venture from Ford and Microsoft takes in-car computing to a whole new level. SYNC does hands-free voice-calling, reads text messages and offers real-time traffic updates. It damn near does everything except tell you where the bad guys are.
The function we’re still waiting for: Offensive capabilities like missiles. KITT got major firepower upgrades over the course of the Knight Rider TV show and there are times when we'd like a laser or grappling hook came standard with our ride. You ever been in LA traffic during rush hour? Yeah, then you, too, have dreamed about what a few missiles would do to those bottle-service douchebags two cars ahead of you.