This is an exciting question and one that many Anthropologists have spent entire careers seeking to answer. Considering all of the distinctions between cultures, it may be appropriate to say that the one thing all countries have in common is ... culture!
Anthropologists like to say that anything that isn't biological (and coded in our DNA) is cultural. That may sound redundant, but consider the multitude of ways in which culture helps us adapt and survive. Humans are highly social beings, so culture accounts for actions which contribute to survival beyond the basics of eating, drinking, sleeping, and having shelter. The ways we eat, drink, sleep, and take shelter are influenced by culture, though.
It may help us to understand the universals of culture by breaking down some of its major aspects. This includes:
Language. One of the ways cultures distinguish themselves from one another is through the languages we speak. Language is heavily connected to another aspect of culture.
Identity. One has to identify as part of a culture to be a part of it, though generally it is required that other members of this culture acknowledge the person as a part of it as well. Identity may be bound up in beliefs about ethnicity, race, religion, and gender. Some identities don't exist out of the context of their culture, but all cultures share a sense of identifying or belonging to a group.
Food. All cultures employ some sort of subsistence strategy to acquire food, which may then be transformed through cooking, preserving, or other forms of presentation. Often, when we talk about culture or identity, we may describe foods or food-related behaviors that are distinctive to a group.
Art. All cultures experience some degree of artistic expression. Humans generally have leisure time in their lives to create beautiful or expressive things or to decorate objects which are primarily functional. Even if all members of a culture do not create art, they understand the shared set of symbols which contribute to the meaning of the art.
Belief systems. Here, I use the term "belief systems" to refer to any way of thinking which helps us make sense of and organize the world around us. This may be religious, scientific, or even folk-belief. Every culture on Earth has a way of thinking about and explaining the world around us. Some belief systems are shared around the world, like major organized religions. Others may be very localized--for example, does your family or community have any special means to try and bring snow or rain? Do you know any urban legends from your town?
Unfortunately, we must speak very generally about the commonalities of culture in countries, but perhaps someday you will join the field of Anthropology and answer this question once and for all.