see i would sort of expect them to pack up after they play as just part of playing, and not as actually one of their jobs, as otherwise you would be picking up after them all the time if they just walk away from games they have started etc.... i suppose i see jobs/chores as additional things that need to be done in the house, not just relating to a mess that they have made, but maybe i am a hardar$e!!!
either way i think reward charts are a great idea, haven't used them yet, but will do when she is a bit older for bits and pieces....