Cargo options for my bike!

Over the past few weeks, I've done a lot of research on different ways to carry things on my bike. The most obvious thing would be to just carry everything in a back pack, but I don't like having a bag on my back throwing off my balance, particularly when going to work involves a big hill with a narrow, bumpy road and a sharp-ish turn in it. Also, it makes my back sweaty. So, I've turned to other means:

Milk crate, pannier, bottle basket

Milk Crate
I've found the crate is a good general purpose mode of transporting things. It's very secure, and can carry a lot--more than any of my other options, actually. In addition, I don't have to worry about leaving the crate on the bike, whereas I'd have to carry the other options with me wherever I went. The main disadvantage is that because of where it's positioned, putting too many heavy things changes the center of gravity of the bike. So, my primary use for it has been for running quick errands. I can throw a purse and a sweater in there and go to the market to pick up a couple of odds and ends. It gets a bag of vegetables or a box of pastries home very nicely.

Pannier
I got this bag mainly so that I could carry my laptop and papers into work. I found that putting these things in my regular backpack in my crate made my bike more likely to "take off" (it's heavy high in the back, so the front wheels tend to lift off the ground a little). This bag is just big enough to hold my work things, and even gym clothes if I plan appropriately. It has a rubber bottom and a rain cover, to keep things dry in various conditions. An added handy feature is that the straps convert to back pack style. It's actually so compact, and I can hardly feel it on the bike even with my laptop and clothes in it--sometimes I look back just to see if it's still there!

Bottle Basket
Perhaps the least necessary of my cargo options, the ideal use for this basket is carrying tall, heavy things that I wouldn't feel comfortable transporting in my crate, e.g. cartons of milk or juice, other things that throw off my balance. I suppose I could carry some of these in my pannier, but this basket feels more secure: it has two arms that hook on to the rear rack, and I use a bungee as well since I travel some very bumpy roads. It's less fussy to get on and off, as there's no messing with clips and tucking away straps and flaps. It's also roomier than the pannier, which can't really take a full load of groceries. Of course, the real added value of this bottle basket is that I can hang it on one side of my rack while hanging my pannier on the other. So, if I wanted to load up on heavy and tall items as well as a regular load of groceries, I wouldn't be limited to choosing either my crate or my pannier.

One thing that might limit me is the 10kg max load on my rack; otherwise, I might attempt this:

Something I'd never actually do

How to attach a milk crate to your bike (nuts/bolts/washers method)

I cannot claim any credit for this, since my only role was insisting on having a system such that my crate is easily removable. The whole thing was engineered by D, who figured it out without even looking anything up--his do-it-yourself skills never cease to amaze me. I also found that if you wheel your bike into Lowe's and park it in the hardware aisle, nobody bats an eyelash.

So there are actually a few websites out there that describe different ways to attach a crate to the back of your bike (D may not have needed to research, but I did). The approaches I found (via Google), and why I rejected them:

1. Zip tie system - seems like the crate would be very secure, but not really a removable/re-attachable, my #1 criterion
2. Bungee sytem - in theory removable/re-attachable, but seems like a pain if you're not well practiced in bungee-ing things down; also, concerns that it's not as secure, and bungee may snap
3. Two metal plates, nuts and bolts - didn't actually see this until I started researching this post, and it's closest to D's system, but it's not removable/re-attachable 

Now, D figured that I should be able to take my crate on and off the bike without having to use any tools, and that the final product should be pretty secure. He came up with a system in which we attached bolts permanently to the bike rack (see order listed in picture caption). We were really lucky in that my bike came with a rack that had an aluminum plate attached, which had pre-drilled holes. The rack worked out really well for our system--D said it seemed like the rack was made to have a crate attached to it!

Bolts, flat washers, slit lock washers, hex nuts, and threadlocker

To attach the crate, you center the crate on the rack with the bolts threading through the holes in the bottom. Then you put a fender washer onto each bolt, and secure the washer with a wing nut. 

Fender washers and wing nuts

And there you have it! To remove it, you just undo the wing nuts and take the washers out. 

Attached crate

The crate is actually pretty secure with the washers and wing nuts alone, especially since we put three bolts in place. However, it still rattled around a little when I went for a ride, and I wanted just a little more security, so I also bungee it down. There's no complicated looping; the cords come in packs of two, so I just run one cord through the front of the crate, and the other cord through the back; the cords hook directly to the rack by the rear hub.

Optional but recommended: bungee cords

The bungee cords add some time to the attaching and removing process, but on the whole it's a quick and easy couple of minutes. I've ridden my bike through some bumpy roads, and it's very stable. I think it's a pretty nifty system, though admittedly having a rack like mine helps a lot. =)

Edited to add: Here's a diagram of the different components of the attachment system, BUT I forgot to draw in  a flat washer that goes between the rack and the bolt. Oops...

Drawn in Paper by Fifty Three, my favorite drawing app ever