You didn't mention your grade level, but I can tell you are not well prepared for this speech. You should read "Dress For Success" by John Molloy for lots of examples. It takes a lot of reading to become aware of what a fuzzy word like "culture" really means.
Culture has roots in an ancient word for a plow. Related words are cult, cultivate, colon and colony. A culture is defined by its more's. When two or more people live in the same area they have to adopt some rules about who does what to whom. Any such rule is called a more', French accented e pronounced "mor-ay". The adjective form is moral, and the habit of following more's is morality. More's are arbitrary: they do not have to be right, only accepted. Another group on the other side of the river might have very different more's.
In many or most cultures looking directly at someone is considered an attack. American slang has the expression "shifty-eyed", which originally referred to Injuns; they would not look directly at someone when they talked to them. Americans of European descent had the opposite custom, that a person who could not look directly at them was not trustworthy. That is what we call "culture clash". So a "shifty-eyed Injun" would be considered a good fellow in his own culture, but have no credibility in the American culture.
The symbol of competence is the lab smock. Imagine a tv commercial for tires: a car is following a truck. Men on the truck are throwing junk in the road for the car to drive over, to show how reliable the tires are. The men are wearing lab smocks. A man in a lab smock is a highly trained professional. Without the lab smock he is a grease monkey.
The symbol of character is shiny black shoes. Military men have a lot of traditional symbols, but the one item that is never forgotten is shoe polish. Shiny shoes show people that the wearer is in the habit of taking care of details. According to John Molloy, there are people who will refuse to do business with a man whose heels are worn, even slightly. They have demonstrated that they can not take care of details.
It is undergrad college level, the speech is only 3-5 minutes and has to touch these topics but not go into too great of a detail. The goal is to have a prop for each subtopic to make it more memorable. I have a rough draft of the speech and a week to work on it. It is a speech on how credibility is important in a persuasive speech using the 3 subtopics. I do like some of your ideas