So I had this dilemma: I commute in work clothes and often go to places other than my office, so when I get to my destination, I don't have a place to stash extra stuff (aside from a coat and maybe a plastic bag with lunch in it). And I'm a lawyer, so I need to carry a bag that looks at least borderline lawyerly. And riding in a suit jacket requires a more upright position, which makes my lawyerly-enough all black messenger bag uncomfortable to carry. The solution, obviously, was to get a briefcase pannier like this one. The problem was that a new briefcase pannier would cost money, and although I'm a lawyer, I'm a public interest lawyer with two kids and a mortgage, so spending money is a no-no. So I made an attachment to my bike rack that allows me to strap my regular work bag on securely in pannier position:
First, I took one square wire grid from one of these shelves:
(Why? Because I had the shelves lying around and wasn't using them.)
Then I bolted it to my rear rack:
I used the lids to some old storage bins to hold the bolts in place. This is not an elegant solution, but it is good for me because I had the lids lying around, so no money was spent. U bolts would have been a nicer solution.
Most of the bolts I used stick inward toward the rack, but two at the bottom had to stick out so they wouldn't interfere with the spokes. So I clipped them short and covered them with black and orange hockey tape. Shorter bolts would have been a nice solution, but, again, no money = use what you have.
I also reinforced the connection between the wire grid and the rack with some clothes hanger wire at a couple points, just to be safe. The grid is sticking up higher than the level of the rack because I have big feet, and my heels hit panniers if they are hanging from the top of the rack.
Finally, I added bungee cords and a bag, and voila:
So far, it works really well. I rode 25 miles during my work day on Tuesday and the thing performed flawlessly. Today I rode to work with a heavier load that included a laptop (well padded, of course), lunch, and rain gear (in addition to my usual papers, pens, and necessary bike tools), and it was still rock solid.