Classes you wish you took before Grad School

I'm currently a junior who's done with pretty much all my graduation requirements except for my capstone. With that being all I have for my senior year, I was wondering if those who have done grad school/are currently there had suggestions for what to take in the next 2 semesters (or if it's better to graduate early and use that extra semester to do something else). I'm interested in pursuing something in Polymeric Materials or Microfluidics. I've been considering these classes thinking they might be useful but open to others:
- Polymer Physics
- Probability
- Stats
- PDEs
- Orgo II
- Intro to Modeling and Simulation

side note*: I'm not paying tuition so there's no financial cost to doing the 2nd semester of senior year