Here's a definition of culture from Wikipedia:
Culture has been understood as a flux of phenomenon that has presuppositions and foundations from their hunter-gathering and nomadic traditions to cultivation.
Dictionary.com has an interesting definition (#5)"
the behaviors and beliefs characteristic of a particular social, ethnic, or age group: the youth culture; the drug culture.
Many of the presuppositions that we have about our culture come from our economic position. For instance, preservation of the culture is often the concern of the upper class since it serves their needs very well; on the other hand, the lowest classes may not have the same attachment to culture becuase it does not serve their economic needs as well. As has been noted, this is something that Karl Marx wrote about. He thought that the conflict between these two "cultures" in one society, would inevitably lead to revolution, and it often has. In many countries, however, the middle class has served as a buffer between the 2 classes, although this is not its main purpose. The middle class, while not having all the cultural advantages of the upper class, is a lot better off than the lower class, and, in theory at least, entry into it is available to members of the lower class given enough education, work, etc. And since the middle class has a serious stake in the maintenance of the status quo culture, they will defend it against threats from the lower class.
Its difficult to get a class to buy into a culture if they spend all their time worrying about their next meal. There's is an interesting discussion of this in "The Legend of the Grand Inquisitor." The Inquisitor notes that hungry people have no free will, and without free will there can be no interest in culture.
This sounds like an excellent question relating to Karl Marx or Marxist thought. In this vein, I will try to answer it as a true student of Marx would. "Material" conditions can refer to personal wealth and consumer drive to acquire more wealth. Such material conditions drive "culture" and what is socially acceptable and coveted. In order to understand this, we have to go back to an underlying assumption that all of societal interactions and structure are based on economics and the acquisition of material wealth. If we presume to believe that material conditions influence culture, then we have to accept that what society values is based on economic value. If this is valid, then we accept that the prevailing economic system of capitalism values money, and its culture mirrors such material value. (Why would a capitalist society, predicated upon making money, subscribe to a culture that does not reflect this idea?) The material conditions that influence, determine, or dictate culture are the ones that drive acquisition of wealth. Ownership of the means of production (the manner by which to gain much money) and the drive to produce and create more wealth drive what is represented in culture. For its part, culture values wealth, power reflects wealth, and social structures are organized by wealth. If we think about it, this is fairly valid. Culture values elements that cost money and represent wealth (The highest caliber of appliances, clothing, automobiles, and personal items all cost money and in order to own them, one has to possess a certain level of wealth.)
Thus, the conditions that determine culture becomes capitalism's desires to keep and create more money and have its culture reflect this.