• Change nutrition habits for people to consume more vegetables and reduce meat consumption  

Sometimes trees can be planted that draw up nutrients from the subsoil, which is too deep for the roots of most crops. Then the leaves of these trees can be used as fertilizer. This has been done to raise corn yields in Africa. It helps even if farmers are too poor to buy commercial fertilizer. Including legumes among the crops may also help, since that renders atmospheric nitrogen available. In rice fields fish such as carp and tilapia can live on algae, which is hard or impossible for people to harvest directly. Being cold-blooded and with the buoyancy of water supporting their weight, they can convert more of their food to edible calories than warm-blooded livestock, and their food (algae) is hard or impossible for people to harvest anyway.

This is a rather complicated question to answer. First, it is not clear what maximizing nutritional level means. There is a significant issue with over consumption globally, with more people globally being overweight than underweight. I also don't follow the cost trade-offs between nutritional interventions and military spending and conflict containment. Conflict clearly has a negative effect on development and nutrition, however, it isn't clear how effective investing in military spending or conflict containment is on reducing conflict. To do this kind of an exercise you would need some relationship that gives you the effect of $1 additional dollar on conflict containment on reducing conflict, and what the effects of reducing conflict are on nutrition.

As for maximizing nutrition, would seem to assume that more is always better, when in fact, after a certain point more can actually be a bad thing. It is also true that the health risks of being overweight, are less than that of being underweight. So given the choice between these two outcomes having a bit more consumption that ideal, is probably better than having too little. Maximizing nutrition, is not the same thing as "maximizing" welfare or positive health outcomes.

A good starting point for the nutrition side of this question would be to define a broadly healthy diet. The WHO has some broad measures that you can use. The UN's definition of Food Security is also a good one to keep in the back of your mind (Composed of four pillars: 1) Food Supply; 2) Food Access; 3) Food Quality, and 4) Resilience of all three across time).

Generally, a more diverse diet is better than a less diverse one. And in terms of health outcomes and sustainability, a diet that is predominantly plant based is also preferable to one that is more heavily dependent on animal products.

Hope that helps