I have a rack, a basket, and a waterproof pannier and this proves most versatile on my cross bike. I have a bunch of braze-ons but even when I had another style rode bike, I used c-clamps to attach the rack to the frame for light loads. Right now, I can carry a ton of weight on my bike no problem. I have the Wald basket seen above and it works great for little loads. I also carry a bungie to use the top of the rack if necessary when grocery shopping.

I know lots of people use backpacks or messenger bags and I have tried that but it never worked. In Missouri, for most of the months you can commute, it is too hot to have a black pack on your back. It also makes it hard for short people like me to see over my shoulder or to use a glasses mirror. Having a rack is awesome because I can attach basically anything to it and can easily bring my computer into work.