Mechanical - bags that fit on the rear rack
You will need bags to carry stuff on your bike. It's hard to know how big or how much to spend. You can also look at messenger bags Chrome makes a (huge) one I own. If you do construction, have a large family, or play a large musical instrument, look at the xtracycle (numerous threads). If you have only one set to start I would go with the Oyster buckets.
Oyster buckets $80 per pair, $40 for one
http://www.cobbworks.com/index.htm
BF Thread
http://www.bikeforums.net/archive/index.php/t-60786
$3 DIY
http://www.makezine.com/blog/archive...for_bikes.html
Duct tape panniers
http://www.makezine.com/blog/archive..._panniers.html
Bulletproof, literally
http://www.advrider.com/forums/showthread.php?t=17843
DIY Panniers
http://scicomp.ucsd.edu/~spav/play/panniers.html