You do. I always recommend, "Ride to Work," by Roni Sarig and Paul Dorn, as a primer for the budding commuter. It is inexpensive and full of all the right info.

As a commuter your motto should always be: Make do with what you have.

Of course, some things are a must:
- Good lighting, if you will ride at night.
- Flat and roadside repair tools
- Storage and carry gear, if you must bring stuff.
- A helmet, if required or desired.

But nothing says you cannot wear the warm clothes you already have when the weather turns cold. You can use the backpack that is in the closet for carrying stuff. You can shop at WalMart or the thrift store, if needs be - I do both. One of my favorite riding shirts is a hockey jersey I got at the thrift store!

Commuters are lucky... they don't have to succumb to the snobbery that most roadies feel compelled towards. Their main goal is transportation on a bicycle.
This leaves them with a lot of the practical, common sense that the road warriors have left behind.

Go to Paul Dorns commuting website and so some reading: http://www.runmuki.com/

My advice is to stay off the sidewalk and assume your place as part of traffic. Learn to work with and among drivers, as opposed to being adversarial with them. Always look ahead, always ride like you're invisible and above all - plan to have fun. Then get out there and ride!