Helmet, lights, and a small mechanical kit (tube, tools, patches, pump/co2). The rest of the gear you will want will come to you in time. If you end up carrying alot of things, ditch the backpack and get a rear rack w/ trunk. Also, while you should try to have the confidence that you can get yourself out of any situation it doesn't hurt to have an alternative. Get familiar with your local bus routes, and carry enough change for a one way fare. Many modern buses have bike racks. In 8 months of commuting, I haven't used the bus once, despite flats and other mechanical problems, but it's handy just in case.

Also, eat right. Fruits, nuts, fiber. It will make the ride better/easier and you will start to see the benefits of riding much faster.

Keep it up!