Here's a funny thing: Commuting by bicycle is easier if you have a car. You can get to work on your bicycle and then use the car to do your shopping in the weekends and other stuff like, I don't know, visiting friends or something in the evenings. If a bicycle is all you've got, on the other hand, you can't suddenly decide to do a lot of stuff at once. If you want to visit someone, you had better do it on your way from work because once you're back home, you'll be too pooped to go out again.
This is one of the reasons I'm so obsessed with load carrying on bicycles. A bicycle without a rack carrier is not really a mode of transportation, it's a toy on par with a trampoline or a croquet set. But even a rack only goes that far. Once I've stuffed my panniers for a set of decent "civilian" clothes and some groceries, there's not a lot of space left. I've done quite a lot of touring with front- and rear panniers, and you really can take a lot with you that way, but packing takes a lot of time.
Spacious and accomodating as the bags on my long tail bicycle are, I could carry even more if I added a pair of "Wideloaders", essentialy kind of shelves that run along the extended rear part of the bicycle, from slightly behind the crank and past the rear wheel.
I made some myself with som dowels, plywood and hose clamps. The advantage is that carrying bulky items is now a lot easier, and even when I don't have that much to freight, packing no longer requires incredible dexterity and four hands because stuff can rest on the wideloaders while I fasten them to the bicycle.
Picture set of the process here.
Much to my delight, this humble piece of carpentry has been featured on Bikehacks and The Xtracycle Gallery.