What would be the best use of my 30 weekends?

I am working in a company that is good, but the work I do is not interesting for me. I like working on C/C++/Python/Ruby/Linux (you get the idea). I will most likely leave for higher studies in six months.

In the meantime, I get some time every weekend or so. I have realized that this free time is very precious, and I would be grateful if you could help me decide how to use my 30 weekends the best possible way. I am listing down some options that I think I have. Feel free to suggest anything:

1. Focus on a web-based app idea that I have.

+ A low-risk time to take it ahead

+ Learn loads

- Would not be able to give it enough time.

2. Do some open-source hacking / freelance projects

+ Contribute to FOSS projects

+ Can pick-and-choose work

+ Learn a lot of varied things

- Might not be very significant

3. Learn Guitar

+ Will add to my personality ;-)

+ Free up my mind from other things for some time

4. Take up Kick-boxing or other martial arts

+ This is purely for not getting intimidated by anyone in the future. ;-)

5. Take up Meditation / Yoga

+ A disciplined mind in harmony with the body can do wonders

- Requires long-term investment of time to show benefits.