Moved to Chemical Engineering sub-forum from Employment and Careers.I think especially with career choices (e.g. should I do this as well as this...?), your choices need to be relevant to your future field. Ask yourself this: am I going to really need 'Mathematical & Computer Sciences' or 'Finance' in my future career?
More specifically, a discipline such as Computer Science is one where you need a genuine interest in computers (more specifically, programming, algorithms and so on). I can't tell you how many people i've seen drop out or switch out of IT/Computer Science related degrees simply because they thought 'oh yeah, it has the word Computer in it, sounds like a load of fun!' and then reality sinks in
It's only worth the extra year if you'll actually put that second degree to use in some way. I would stick with the single to be honest. That's just my opinion though
Do you have career counsellors at your school that can assist with this kind of thing?