There are a ton of instructables on making kitty litter bike panniers and most of them are really awesome. I used many of them as the base for this instructable which is intended to show you how to make these cheap panniers in minute detail. I haven't yet tested these strenuously yet, but they're cheap enough that even if they fall apart after three months it was still worth it.

Step 1: Materials and Tools

There are a few things in this picture I did not end up needing, ignore the tape in the blue roll, and S hooks.
You will need the following:

Cost:
This project cost me $18 for the parts from our local hardware store. I had all of the tools already, and the kitty litter buckets were free.

Materials:
2 Kitty litter buckets, I got mine for free. If you don't have cats try asking neighbors and community members, somebody may have them lying around.
2 Bungies, mine were 12" I believe. You want them to be able to stretch halfway around the low part of the bucket.
4 Hooks, I found mine at the local hardware store. The hooks need to have screw holes and be big enough to fit over your bike rack.
8 1/4" x 3/4" bolts to hold the hooks on. The bolts dimensions aren't important, just make sure they fit nicely in the hooks you buy.
4 1/4" x 3/4" bolts for the bungies to go to.
8 1/4" nuts to go with the bolts above. Again, don't worry if they're not 1/4" just make sure they match the bolts you buy.
8 1/4" nuts to help hold the bungies in place.
8 Large washers to help keep the plastic safe from the bolts holding the bungies.

Tools:
- Measuring tape
- Sharpie
- Exacto knife
- Wrenches that match the size of your nuts and bolts.
- Drill and bit that matches the size of your nuts and bolts.
- Eye protection so bits of plastic don't get in your eyes.
- Duct tape or electricians tape.

The rest of this instructable will walk you through making a single bike pannier. You can do both at once, or do one all the way through and do the next one all the way through. I chose the latter method because it let me figure out the best way to do each task, then put it into practice.

Step 2: Measure and Cut for Hooks

The first thing you will want to do is decide how you want your bike panniers to sit on your rack. I wanted mine to sit level with the top of the rack so I can put large objects across it. Then you'll need to experiment with how far apart the hooks should be so that they will work on your rack. I did all of this by dangling the hooks off the rack and holding them to the kitty litter bucket until it looked pretty close.

Once you have an idea of both how high on the kitty litter bucket and how far apart the hooks should be to work with your rack, use your sharpie to mark the bottom center of one of the hooks. I then measured to that mark, and used that measurement for the other side too so they match. Draw some lines to the sides of those marks on the raised lip of the bucket, we're going to cut that part out.

--BE CAREFUL THAT YOU GET A BUCKET FOR EACH SIDE! If you don't think about it it's very possible to get two buckets for the same side of your rack.--

Take your utility knife and cut out the lower rim where the hook will go. I cut down each of the sides first, then made a lot of small cuts on an angle so the plastic came away in tiny chunks. This helped me avoid breaking my blade.

Once you've cut out the lower rim I put a hook in your newly cut slot, to test that it's big enough. Once your hook fits, make sure it's vertical on the bucket and trace the sides of the hook on the second rim of the bucket that the hook is hitting. Cut that rim out too. Once you've cut both rims down the hook should sit pretty close (within 1/8") to the bucket.

Next you'll want to do the same for your second hook. This one is different because the lid of the bucket will be in the way of your hook. Simply cut out about 1/2" of the lid and you should be fine. The hook won't sit as nicely as the other side, but when you use the bolts to fasten the hooks on any gaps will disappear.

Step 3: Tape and Install Hooks

You've done the hardest part already. The next thing we're going to do is put some duct or electrician's tape on the hooks. This helps prevent the metal hooks from scratching up the paint on your bike rack. You can skip this if you don't care. I ripped a 9" piece of duct tape in half lengthwise and wrapped half around each hook. My picture for this is a little confusing because I wrapped my hooks AFTER installing them. That made it more difficult so you should wrap your hooks BEFORE installing them.

The next thing we're doing to do is drill some holes and install those hooks. To find out where you want your holes see the second picture, just hold your hook in place and use your sharpie to mark the center of each hole. Then use your drill to punch out each hole. Just a heads up, the plastic tends to grab the drill bit and yank it when you get through the plastic so be ready.

Once you have drilled all four holes simply mount the hooks using your nuts and bolts. I aimed the bolt heads out because I liked the way it looks. You can then use your wrenches to tighten them down. When you tighten the bolts the hooks should snug right up to the plastic and mostly remove any gaps.

Once you've tightened down your nuts, go out to your bike and hang this thing off the rack, just to make sure that it works so far.

Step 4: Think and Install Bungie

The last thing that we need to do is install a bungie cord on the bottom of the bucket to hold it down and against your rack so it won't bounce around when empty. The best place to put the bungie cord is going to vary depending on your rack. What I did was hang the pannier off the rack and mess with a bungie until I found a good height to put it at so it looped around the rack in a way I liked.

I then drilled a hole at that height in the center of each of the short sides of the bucket and put a screw in each hole. These screws have a nut and washer on both the inside and outside (see pictures). This lets it spread some of the force out over more plastic. I then hooked the bungie around the part of the bolt sticking out, looped it around the rack, then hooked it to the other bolt. My bungie ended up being pretty tight, which is nice because it holds the bucket firmly.It

Step 5: Ride and Enjoy

You can now test out your new pannier and make the other side if you haven't already. Let me know if you have feedback for me or are unclear on some steps. This instructable has yet to be edited so it may be rough in places.

I left the handles on the buckets so I can carry them easily when I take them off the bike. They're kind of annoying when they bounce around while I'm riding, but they're more useful than annoying so far.

The final thing I want to do with these is paint them so they're no longer that yellow color. I'm thinking that I will use spray paint of some sort, but I'm not yet sure how well it'll stick to this particular plastic. Let me know if you do paint, I'd love to see a picture.