I've never had trouble crossing the border with a whole whack of instruments in the car, although once we were asked if we possessed any "narcotics". When we were done falling about laughing, we realized the U.S. officer-type person was quite serious and answered him seriously, at which point he favoured us with his opinions on Canadian wacky-terbacky and waved us through. If we say we're going to a folk festival (that is, if we are) we always say we are not performing for money. Otherwise, we just say we're visiting friends -- also true. Either way, we have always been waved through.