Most of these instruments could be automatic and be played by the movement of the car:
Drums facing down toward the road with hard rubber tipped drum stick on a hinge so that it bounces between the road and drum. Clock-like gears could be used to create different rhythms.
Truck-flutes (see idea of this name) -- wind instruments with funnels facing in the direction of travel, with serialized mechanical Gatling scores incorporated into their structure.
Caliope-like instruments working on wind or the movement of the car.
Obligatory megaphone for sing-along.
This could be a more-than-one-weekend project.-- JesusHChrist, Mar 02 2014 Truck Flute Truck_20Flute [JesusHChrist, Mar 02 2014] Ok Go http://www.youtube....watch?v=MejbOFk7H6cAwesome music video. [RayfordSteele, Mar 06 2014] Would the driver be playing the tune, or would the car just be an automatic play-back device like a pianola?-- pertinax, Mar 06 2014 I was thinking the driver would be singing along like a one-man band.-- JesusHChrist, Mar 06 2014 You must watch the Needing/Getting music video by OK Go. These guys should be honorary halfbakers.-- RayfordSteele, Mar 06 2014 random, halfbakery