Think along the lines of nutrician labels, calorie amounts listed on resturant menus, "sugar" tax on soda, farm subsidies, etc.
There is currently a massive subsidy for corn producers in the United States, which is one reason why High Fructose Corn Syrup is much more economical than sugar when it comes to added sweeteners in processed foods. Ending this subsidy, at least at the current level, might discourage such a widespread use of HFCS. We could then direct those subsidies towards locally grown produce, which would encourage the consumption of fruits and vegetables, as well as greatly reducing the amount of energy required to get food to the American dinner table.
I am not too sure what current information it is necessary for producers to provide to consumers. In Britain we have seen in the last few years more and more information that needs to be provided in supermarkets so that buyers can have all the information necessary to make wise buying choices regarding their food. However, as #2 makes clear, there is always the concern of governments stepping in and telling consumers what they should and should not be buying. In Britain, we call this a "nanny state" where the government treats us like children and oversteps its power. Certainly, there is always more that can be done to make people aware of the dangers of eating unhealthily, but at the same time I don't think governments should ever be able to prevent people from buying unhealthy foods.
First of all, I would encourage you to follow the link below and read the articles that can be found there on the topic of things the government could do to promote health.
Second, I think that there are many things that government could do to encourage people to shop and eat more healthily. However, it is not clear to me what government should do. Government intrusion into people's eating habits is something that is not completely consistent with American values.
What government should do, in my opinion, is to provide unbiased information to consumers. The government should give consumers information about what kinds of foods are good for them. The government should require nutritional labels on food sold at stores and, perhaps, on food made at chain restaurants where the menus are always relatively similar and the burden on the proprietors would not be too onerous.
However, the idea of taxes on foods that the government deems to be bad for you seems like a step too far. I would argue, though, that private insurance companies could promote better shopping and eating habits by charging higher premiums to people who do not keep themselves in decent shape.