You want lots of butts in the seats at the community cleanup or the first PTA gathering of the year? Advertise that a $50 prepaid debit card (or a couple of $25 ones) will be given away. Advertise it extensively. Sure, it would be nice if people would attend such things without coaxing, but be realistic: If someone’s on the fence about attending (“Do I want to get up that early on a Saturday?/Be out that late on a school night?”) then the chance of winning might tip them over into Do The Right Thing territory.