In terms of prerequisites, if you want to keep your options open it's best to do Chem and Methods (as coblin said) and maybe Spesh, because that is required for some courses. You should also invest a good amount of time into English. As for useful courses, apparently History Revs is closer to a university subject than most others. And obviously, whatever you're interested in studying is a good idea to start off with. Looking back on high school, all of my subjects have come in handy because I've just continued with my interests. Even methods was useful (despite the fact I do no maths now) for things like set theory as well as the ability to solve problems logically and systematically. Economics was also very useful for when I did political science. Lit also helped my writing ability.