I remember a few years back, a sushi restaurant in LA was taking live fish and cutting them up fresh in front of customers (only those who wanted it of course). THey became very popular among discerning Japanese until someone got upset about it and they were charged with animal cruelty! I don't remember all the details, but I do remember, the restaurant was forced to stop. I just remember thinking, what difference does it make where the fish is killed? Humans are weird sometimes.
Anyway, I'd go for the area where we would get most support and most bang for the buck, and that would be with education. Try to make labeling laws to force them to be more honest on what goes into the food. Most people live in denial. Truth in advertising would make it harder for people to not notice how unhealthy processed foods are. And for grains, I would push their basic lack of nutrition. That is something you just can't argue about. Grains have very little nutrition and lots of calories.
On another front, I would continue to educate about weight loss and diabetes control. These are already where more paleo style eating have made huge inroads because diabetes and excess weight are major issues to most of the public and paleo works really really well for those. In fact, even main stream medical is coming around nicely about the importance of cutting carbs for diabetes and eating less processed foods. THe momentum is really starting to gain on those issues and it is where we are strongest. And although cutting carbs for weight loss is no longer the big trend it was for a while, I still know a lot of people who know and do not argue with the fact that it really works for weight loss.
Of course, there are many other areas I think are very important, but I would suggest we push hardest on those things that people are more able to understand and agree with. Once people have better understandings of the situatoin and what works, I think it will be easier for them to take a new look at some of the other issues as well.
Right now, there is no money for parks and even if there was, you could run into liability and lawsuit issues if making things for climbing. This is becoming more of an issue every year. And emotionally, most of the city dwelling public in the US will not get behind the idea of home butchering or loosening standards on that kind of thing. Just because the idea will gross them out. (heck it even grosses me out a bit even though I logically understand the health benefits) As for subsidies in general, arg, I am against them in general, but they seem to have gotten rather entrenched. It's the quiet little secret that all the politicians like to pretend is not there. Perhaps the trick there is to just educate on healthfulness and lack thereof and perhaps the demand for corn will go down and growers will shift to planting something else, or they will find some other use for corn like making cat litter or whatever.
But I think overall, the trick would be to target areas where large segments of the public would quickly and easily agree with emotionally and would really get behind us on. If you want to take down a wall, the trick is to target the weakest part of it first.