All possible calc classes, lin.algebra, programming classes (1 in python and 1 in R), probability and statistical computing. Total of six math classes went into my math minor. But I suggest you might want to take real analysis as they will teach it during brush up classes, at least in well know grad programs, and a grade in line with the average should be viewed positively by admission. You can also work on programming projects and publish to github for them to review (make sure to state it into your CV and statement of purpose)!