Stokes's theorem/Green's theorem. Important near the beginning.

Familiarity with argument using continuity, connectedness and compactness. For example, if you need to show why a continuous function on a closed disk has a point with minimum absolute value it should be obvious to you.

Basic differentiation, integration, and summation techniques. Just calculus stuff, nothing too advanced.

Convergence of functions. You don't even have to worry about all the different kind of convergences, just be aware that they exist. Most of the time you only use uniform convergence, and if you encounter anything else it probably means you need to change your approach.

Laplacian, possibly important but depends on course. Because of relationship between complex analytic function and harmonic functions.

Complex analysis is a much more computational course compared to the proof-based fundamental-based real analysis. So not a lot of Real Analysis will help you. Your calculus techniques are much more important.