Have you ever wondered what the Harry Potter characters would ever do if they were living in the Muggle World? I can't answer many of those questions for you, but I can shed some light on what the characters would major in, if they went to college.
1. Harry Potter- International Relations
Now, this one was hard to choose. After Harry leaves Hogwarts, he becomes an auror, and eventually is the head of the whole department. Criminal Justice doesn't feel right for him to major in, since he works with a lot more than that. Since he has to be diplomatic with what he does, and what he has done in the past, International Relations feels best.
2. Ron Weasley- Criminal Justice
Criminal Justice has always been the stereotypical lazy major. There's no denying that people with this major do a lot of work, but laziness is just what Ron was attracted to. He also becomes an Auror after the war for a good amount of time, reinventing the department with Harry, before he left to go help George with the joke shop.
3. Hermione Granger- History and Political Science
Nobody could ever hold Hermoine Granger back from accomplishing great things. After being the only one of the trio to go back to Hogwarts to complete her schooling, she started to work for the Department for the Regulation and Control of Magical Creatures. She changed the world and their opinions of house elves. After that, she became the new Minister of Magic after Kinglsey Shacklebolt. She had to work hard in her studies and possibly went to law school (in this muggle world fanstasy). The best way to accomplish this is to major in History and Political Science.
4. Draco Malfoy- Chemistry
5. Neville- Environmental Science
6. Luna- Biology
7. Fred and George- Business Administration
Obviously, Fred and George open their own shop, so they need Business Admin. But since you don't necessarily need a degree to start your own business, I assume that the twins, much like at Hogwarts, drop out early to open their business.