I agree with a lot of people here, I carry in my bag:

- Spare Tube
- Patch Kit
- Small Multi Tool (http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1)
- Small Pump, decided against CO2 as someone made a good point that CO2 you are limited but if you have arms you have air with pump (http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1)
- Tire Lever
- Presta Adapter
- Also when i go out I always make sure to bring some cash, a credit card, my insurance card, and my public transit card as with this I figure I can get out of most trouble.

I know the basics about how to change a tire and some derailleur adjustments, though I do think I want to learn more so I can be more self-sufficient, especially when I am in trouble.