Best path for a PhD in CS from a top school? In short, I recently got admitted to a computer science and engineering programme at the KTH royal institute of technology which basically is a Bsc. in CS + Msc. in one of a dozen choosable related subjects. My main interests are machine learning, math and finance and would like to eventually work as a research scientist in ML (deepmind if I am allowed to dream) or in algorithmic trading. Naturally, I'd like to do a PhD in CS and although this can definitely change in the future I want to prepare myself for it.

What is the best possible path for me to take academically when regarding employability and admissions to a top PhD program (Oxbridge, MIT, berkley etc.)?

I have 4 options:


Take computer science and engineering degree from KTH and just focus on getting as competent as I possibly can for CS/ML research.
Take computer science and engineering degree from KTH with good grades and take a Bsc. Business&amp;Economics from the Stockholm school of economics in PARALLEL.
Take computer science and engineering degree from KTH with good grades and take a Bsc. Mathematics from Stockholm University in PARALLEL.
Suggestion please


Note that I am referring to two seperate bachelor's degrees in 2. and 3. with a twice the credits/ECTS. I am not referring to a double major.

option 2. has been done before by highly motivated and intelligent students so I know it can be done. This option dramatically increases employability in Sweden especially in consulting but I have no idea how much this helps CS PhD admissions. Furthermore, although enjoyable it seems like a total waste of time as I doubt I will learn anything useful.

Option 3. seems like a balance of option 1 and 3 but I have no idea how difficult this is to execute as I have never heard of anyone doing this. By balance I'm not implying it is the best option, I simply don't know how much weight I should put into employability and competence.

Does anyone of you have any suggestions for what would be a better academic path with my goals in mind?

I realize in advance that this post may come of as naive and that might very well be true. If that is the case please enlighten me on my false perception of reality.

Thanks in advance!
Research experience will help you a lot more in getting into a good PhD than an extra degree. For this reason, I would recommend 1. to meet your goals. 

Additionally, having dual degrees in not a requirement for doing inter-disciplinary research. Working with an adviser that has the relevant experiences, taking a few classes, or reading on your own are all great ways to learn about a second field, and then to start to apply your research from your primary field to your secondary field. You can also transition to your secondary field for your PhD if you choose, even if you don't have a degree in that field. My Bachelor's was Math, I am now pursuing a PhD in Computer Science. Doing extra research as an undergraduate helped me more in getting into my program than taking extra CS classes would have.