EG: Ban any "unhealthy" food from being purchased using public assistance. Require anyone who is on public assistance provide proof of doing 30 minutes of daily exercise. Tie public assistance aid to your credit score. Place monitors in the house so if one is engaging in too much time-wasting activity (video game binges! hours of social media!) your funding is cut.
This could get pretty nightmarish frankly in an Orwellian way, especially if we combine this with the "world is so automated a basic income is absolutely necessary" idea that's floated around here a lot.
Generally, in the states that drug test for "welfare", the results seem to mostly point to a waste of money (typical articles on the phenomenon are here: http://www.forbes.com/sites/judystone/2015/02/17/the-sham-of...). As my above point on reagents, the standard "pee test" involves similar principals; the only way to truly confirm a positive pee test is to send it to a lab for GCMS analysis. This is not cheap.