Also a good option for science electives would be classes you'll see again med school! My senior year I'm taking histology, endocrinology, comparative vertebrate anatomy and microbiology. Med students that had taken the histology course at my undergrad said it kicked their butts so hard that when they took the med school course it was much easier! Having that initial exposure is really good. 🙂
But yeah it also depends on what school you go to. Some other cool courses at my school (maybe at yours too) are things like immunology, virology, pharmacology, and others. Just find something that interests you! Electives should be fun (at least something that you enjoy), which may not necessarily translate as being easy haha.