What are the standard math prerequisites for physical chemistry?
In my experience, the most helpful advanced math courses you can take for Physical Chemistry are Differential Equations and Linear Algebra. Multivariate Calculus is helpful, but not as helpful as Diff. Eq. would be, especially in the beginning. Linear Algebra is very helpful for quantum chemistry, Diff. Eq. is also helpful for quantum, but more so for statistical mechanics. In the comments you mentioned several different Diff. Eq. options - as @permeakra said, taking all of them is a good idea, but ODEs and PDEs will probably be the most useful.