my friend's dad used to wheel back in the day w/ his jeep. he went to a lot of events & tells us about them. some things they did sounded like really fun contests.
like, a timed obstacle course, but the driver was blind-folded & the passenger had to navigate thru the course. another obstacle course - again timed, but the driver had to carry a bucket of water in his/her lap & get through the course the fastest w/o spilling water - the fastest & least amt of water spilled won. (not sure any one wants a soaked seat - maybe modify this one & strap it to the gear basket.)
can't 'member any more right now - but if you like these suggestions, i'll ask friend's dad if he remembers any more.