There are a few things that I always take with me on a ride. As others have mentioned, a cell phone, tubes and CO2 cartridges. I take a mirror with me that attaches to my sunglasses, makes me safer being able to see if someone is coming up behind me. I always carry a Click-Stand in my middle Jersey pocket because I don't like leaning my bike against a wall (link below).

As for money and credit cards, I carry those and my driver's license in a zippered pocket on the back of my Jersey.



http://www.click-stand.com/Click-Stand_Products.html