What are some helpful high school courses for becoming a vet?

You can't become a veterinarian immediately after high school, so the focus is more on preparing yourself to go to college to take the classes you will need to apply to vet school.

Therefore, you should focus on taking the "college prep", "advanced" or similar courses in high school in all the major subject areas (language, history, science, math) as well as a good selection of electives like art, music or a foreign language.