A few years ago I stumbled across a lightweight, clip-on shopping bag called Bikezac made by a Danish company, Cobags. Easily removed from the bike, looking much like an ordinary shopping bag when carried, inexpensive, folding up small, and light enough to take everywhere with you "just in case", it seemed to have a lot going for it. But I could only find online suppliers in the UK and I wanted to have a look at one before buying. So instead I made myself something similar from a supermarket bag-for-life.

Bikezac bags are more readily available today but if you have access to a 3D printer to make the clips and a sewing machine you can create one yourself very easily at minimal cost. Tinkercad is ideal for designing the clips - in fact, this was my first ever Tinkercad make.

Supplies

Polypropylene bag-for-life (see Step 1)

About 26cm / 10" of strong 8mm dowel (or slimmer if using carbon fibre or aluminium rod)

3D printer and filament - I used PLA

Sewing machine and thread

Quilting clips (or clothes pegs / clothes pins)

Stitch ripper (optional)

Small, sharp scissors

A saw for cutting the dowel/rod

Step 1: Choosing a Suitable Bag

Take a tape measure or retractable steel rule with you to a few local supermarkets and have a look at the multiple-use bags available. You want one that's made of polypropylene (PP) - most of them are and in the UK (at least) will probably have the recycling code 5 printed on them somewhere.

Choose a bag that has a seam across the bottom gusset (see photo) rather than a separate piece sewn in to form the gusset. The side gussets should, ideally, be separate pieces of material that have been sewn to the front and back.

The hem around the top of the bag needs to be deep enough to take the dowel or rod you're planning to use, so measure that too. Unless the handles are only stitched through one layer of the hem (see photo), you're going to have to make do with the clips holding the bag to the pannier rack being quite close together.

If you can find a bag, like mine, that has narrow strips of PP stitched over the seams to strengthen them, all the better.

The bag I used was from Sainsbury's and measured approx 46cm wide x 38cm high x 20cm deep (18" x 15" x 8"). You'll be removing the side gussets to leave just a front and a back, then refashioning the bag to make it the same depth at the base as it was orginally, but flat at the top. That stops the bag's opening from flapping about and gaping on the bike, even when it's empty. But it can still take a lot of shopping and will stand upright.

Step 2: Modifying the Supermarket Bag

Unpick the side seams and remove the side gussets, or cut them off leaving a 1cm (3/8") seam allowance if they are all in one with the front and back. (I redeployed my side gussets as a bottle carrying bag.) Retain the seam binding strips, if there are any.

Then, with the bag right sides out, fold the base up between the front and back along the original fold lines as shown in the photo. Hold the side seams together using quilting clips (or clothes pegs / clothes pins) rather than pins because holes don't disappear in this material. Then stitch the seams with a strong thread and a fairly long stitch length, the PP fabric could tear if the holes are too close together. Put the seam binding strips around the seams and stitch again to reinforce them.

Step 3: Making the Clips

The bag is suspended from a bicycle's rear pannier rack by means of two clips. The upper, hook part needs to fit securely over the side rail of the rack while being removable without a struggle, while the lower part is a ring that slides onto a dowel running inside the top hem of the bag. I've attached the STL file I produced in Tinkercad but you're almost certainly going to have to design your own to suit your rack and dowel size. For some reason, I didn't save my final Tinkercad file, only an early version which has the hook part only:

https://www.tinkercad.com/things/3fbaGwb2hnd

But adding the ring at the base is a straightforward matter of adding a Tube shape and then Grouping it with the hook part. The little nub on the hook holds it securely in place on the pannier rail.

To get the ring part the right size, I printed a Grouping of three Tubes, each with a slightly different inside diameter, and chose the one that was loose enough to slide along my dowel/rod when pushed quite hard, but not so loose that it would slip on its own.

When you have a hook and a ring of the right size - you'll probably need to print a few, tweaking the dimensions each time, but the test prints don't have to be the full 10mm depth - combine them to make a complete hook and then print two. I used 20% infill because I didn't want to make the hook part too stiff and brittle in case it cracked when clipping it on and off the pannier rack.

Whole bike clip 5.stl
Download View in 3D

Step 4: Assembly

With small scissors, cut a rectangular window in the inside layer (only) of the bag's top hem just outside each end of the handle, on one side of the bag. (The side with these windows will be the back of the bag that sits against the rear wheel.) However, if your bag has the handles stitched through both layers of the hem, the windows will need to be positioned just inside the handles. Either way, the windows need to be just big enough to let the hooks emerge - see photo.

Now cut your dowel/rod to length. It should be long enough to extend about 12mm / 0.5" beyond the windows you cut - any more and you won't be able to fold the bag up as small as possible, but the ring part of the clip does need to be a very tight fit on the dowel.

Feed the dowel through one window and along the hem until it reaches the second window. Hold a clip in place with its ring in the window and its hook pointing towards the back of the bag, and slide the end of the dowel through it and far enough beyond to allow the other clip to be positioned in the first window. Use a little lubricant, such as liquid detergent, inside the ring of the clip to help it slide along the dowel if necessary. Then slide the dowel back again, catching the second clip. Manipulate the dowel, through the hem fabric, until the clips are evenly spaced on it.

To use the bag, just clip it onto the rail of your pannier rack. If you want to store it or carry it off the bike, fold the two sides in and then fold it in half by bringing the base up to the top.