What do you wanna do with the bike instead of using your car? You can do some light grocery shopping with a rack and some panniers. If you wanna do other stuff, you basically need a lock. I like having a rack and panniers because it makes nearly any situation work. Problem is, it's more weight on your back wheel, which is already taking the stress of you being a Clyde. But since your bike probably isn't a cheap one, it should take the weight fine. You can break the habit of not using the car by putting your butt on the bike seat and starting to pedal.

The commuting forum has all kinds of info on keeping clean after riding. Some people take "sink showers," some people use baby wipes. My commute into work isn't long enough for me to really get sweaty and I don't care about the other places I go, heaven forbid someone sweat, I'm on a freakin' bicycle.