since this always comes up

how to use food stamps?

Apparently not on soda, if you're in New York. But then all kinds of other "crap" is perfectly fine to purchase, why not ban that stuff too?

Since I favor a negative income tax and letting people spend those resources on food (and by extension, health care) as they see fit, I don't see what the problem is if people knowingly and wantonly "waste" money on what amounts to far more expensive sugary drinks and fattening foods. There is some heuristic value to buying food that tastes good and delivers to us some desired pleasure after all, even if it comes at a particular price to our health. What concerns me is that they're not aware of the actual cost of those items and unpersuaded that they could make do with some cans or bags of frozen beans or peas once in a while or some such instead of a bag of chips. Far simpler than banning food stamp use on soda would be things like this

1) Soda taxes or some other "junk food tax" to factor in the social cost of providing additional health care to over-consumed goods of some sort. New York has already been moving on that one. The trouble with this is that I'm sometimes skeptical that most of these goods are actually causing a great deal of unpaid social costs. What they're actually doing is translating wages into health insurance. Which is no fun for healthy people, but healthy people don't seem to account for a majority of the population. There's actually another problem with this though...

2) Price in things like water rights at market rates rather than through food subsidies and price controls. If water is expensive rather than too cheap as it often is in parts of the country, things won't be grown that are less efficient with more water, and things such as industrial scale meat production might be curtailed. And if corn isn't subsidized, and sugar isn't price controlled, fewer things might include "corn sugar", as they want it to be known as now. What we'd end up doing is taxing something we were already spending money on anyway through the subsidies or price controls. It might be, as a matter of public choice theory, harder to end the subsidies than it is to tax, but the most efficient result possible, in so far as making cheap crappy food "less available" to poor people, is likely to do neither. If there's still a demand for cheap crappy food at that point, there are other more persuasive steps that can be taken in a less invasive or less powerful sense than mandated responses through the authority of the state and its social safety nets.