Without knowing what program you've been through, what program you're planning on entering, and what focus or purpose you have in seeking a MS in CS, I can only

Without knowing what program you've been through, what program you're planning on entering, and what focus or purpose you have in seeking a MS in CS, I can only describe things based on the program I went through. A student ought to have studied and understand discrete math, data structures, and fundamental concepts of computing and programming languages. CS isn't about programming, but for your mind to be in the right place and in order to participate in the program you really ought to be a strong coder with at least one language under your belt. Research will almost certainly require significant coding, even if the work is theoretical in nature. Beyond that it really depends on what program you're doing and what your focus will be. In many cases you'll want significant mathematics background, including areas like abstract algebra (important for crypto studies), numerical analysis, experience with proofs (useful for theory of computations studies)...it goes on and on.