I was reading [xenzag's] Dirt Fortified Food idea when this came to me. First, let's all agree that exposure to dirt and muck boosts the immune system (gosh, that was easy). I recently read a New Scientist article pointing out the much lower incidence of allergies among children that had grown up on
a farm or otherwise exposed to animals, so there is some scientific base to this idea.
However, kids in urban environments don't really get exposed to animals much, and good quality urban dirt is hard to find (too gritty and dusty, and too much broken glass). Putting dirt into food raises all sorts of questions - basically it goes against the whole philosophy of the food industry, which tries to make things last longer on the shelf (and not make you so sick) by sterilizing them.
Let's drag in an almost-unrelated fact here: supermarkets make lots of money.
So the idea here is this: Specially trained cows are leased to supermarkets. They are patiently taught to carry shopping in big panniers on their flanks, and (being ruminants) can patiently chew the cud for hours on end while Mum wanders up and down the aisles, and Dad agonizes over which of the nine different types of salt to buy. They could browse in the car park (people drive so slowly, they'd only be hit very rarely). That way, people (most especially children) get the benefits of animal exposure without having to turn our whole food infrastructure on its head.
A couple of fringe benefits, too: Children will understand more clearly where meat comes from. Also, each supermarket could sell its own locally produced milk (unpasteurised, so buyer beware). Third, people might even develop emotional attachment to particular trolleys, promoting more people to visit the supermarket and drumming up extra business!
Poo could be a problem, but since (as I mentioned earlier) supermarkets make lots of money, they can probably afford to employ an extra cowhand to look after the trolleys and clean up after them. With a bit of luck, the superhealthiness of these supermarkets (let's call it Cowco) (or better, Mooco) will drag in so many more people that the new trolleys will easily pay for themselves...