The previous posts explain their answers in a very lucid and clear way. Part of the idea behind how food plays a socially powerful role may lie in the fact that the advertising of food is critical to our economy and social setting. Advertisements about food have always been a part of our history and is part of our society. Any kid understands the McDonald's theme, the King from Burger King or the "5 Dollar Foot Long" Chant from Subway. This helps to create food as part of our social setting and represents a profound influence on our society. Given the fact that food product placement in films and other venues such as sports arenas and airports make food an almost indispensable part of our setting. Additionally, some of the food that is most prominently placed is "junk food," which creates some level of addictive habits. This type of food is so powerfully and prominently displayed because of its consumptive qualities. At this moment, some family is deciding that it is too much to prepare dinner, so "Let's get McDonald's tonight." This creates food, particularly fast food, as a part of our social order, difficult to completely evade.
We are also influenced by our accessibility to cheap food. This makes it very difficult to pass any kind of health regulations, or to enforce those that are already passed. Many Americans remain unaware that USDA inspections are voluntary, & there are no repercussions for a factory that does not adhere to them. Any time a referendum or bill is suggested, powerful food conglomerates (such as Con-Agra) lobby to defeat it. This makes it difficult to improve the quality of our inexpensive food, particularly meat. Hence the outrageous prices for organic/grass-fed beef, or the recent uproar from the egg industries after the passing of Prop 2 in California. the sad thing is that most Americans have no idea of the influence such food companies have over policy and regulations. A very good book to check out is The Politics of Food, which explores many of these issues.
Also, food has influenced our cultural identity. What's more American than apple pie, right? Certain foods are associated with our national heritage, & it's deemed "right" to barbecue or eat hot dogs on the 4th of July. Foods like beef (think hamburgers and ribs) are identified as masculine, and thus vegetarians are often seen as "wussy" or feminine. And we quickly become offended when someone challenges our right to eat anything, even deep-fried twinkies. Even the result of food influences that identity: we are known throughout the world for our outrageous levels of obesity.
In all these ways, in addition to the important points made by the first poster, we as a country are influenced by our food.
It's hard for me to tell the difference between how our society is influenced by food and how our society influences food. But here are a couple thoughts. These are from the perspective of an American, though one who grew up outside the country and whose father is an immigrant.
To me, American society is influenced by restaurant food and especially fast food. Because we have these all these kinds of foods available, our families can, in some ways, be undermined. This is because many American families no longer spend time eating together or preparing food for/with one another. I think this is an important impact.
Perhaps one other impact is that all the food that is available to us helps make us think that we can and should have everything in the world available to us. Growing up outside the US, my family could only eat what was available on the local economy. But here in the US, you can get pretty much anything at any time of year. I think that helps us feel entitled to whatever we want.
But again, it's hard to say if food makes us like this or if we were already like that and that influenced our food.