I loaded Bianca up this weekend with who-knows-how-many pounds of stuff. I dislike having a bag against my back, so I added the rear rack (and later, the awesomely reflective crate) to her before she even came home with me.
In the crate:
4 heavy books
lots of thrifted clothes for a patchwork quilt I am making
1 reflective waterproof rain jacket (which, after an unfortunate incident involving a white shirt, rain, and me on a bike, stays folded in the crate at all times)
2 extra bungee cords
1 8" x 8" artwork
1 thrifted wood basket that may or may not turn into a front bike basket
1 backpack full of various items (brush, wallet, newspaper, camera, phone, yadda yadda yadda)
1 large roll of paper (to recycle into books), attached by rubber bands through the holes in the crate
...and a partridge in a pear tree.
All this without even having a front basket yet. Who says you need a car for a shopping trip?
This is nothing, really. There's a moving co-ops in Portland where people will help you move across town by bicycle. Search "move by bike" at Flickr to see some seriously loaded-up bikes.
What's the biggest thing you've managed to get home on a bike?