This really depends on what your paper topic is and what you have said about McDonaldization. A good summary for a paper like this restates and reemphasizes the points you have made in the rest of your paper. Therefore, what you have to do is to figure out what you are really saying in your paper.
In a previous question, you asked about the impact of McDonaldization on everyday life. If that is what you have written about, you might want to conclude by recapping whether you think our modern society truly is "McDonaldized." You have to ask yourself whether our society has come to emphasize efficiency, calculability, predictablity, and control.
Or maybe you have written about whether these changes are good or bad for society. If so, leave the reader with a conclusion that emphasizes how those changes are good or bad. Either way, you really need to figure out what the point of your essay has been and then write a conclusion based on that.