We have a folding shopping cart which is great, but the original clip was lost (and found, several times, except the last). After loosing it for good, we used string, wire ties, whatever. Very annoying. So I made a simple replacement.
This type of cart seems to be very popular, sold by various manufacturers in various sizes (we got ours from Amazon) but it's basically the same cart, so this might be useful to others.
Depending on the size of your model, you'll probably want to adjust the clip length. All dimensions are in mm. I'm guessing the wire diameter is the same for all carts, but you may want to check. Also, depending on your slicer and extrusion width, you may want to fine-tune the clip width.
Print the STL in the given orientation for strength (do not print flat on it's back, it will likely delaminate under stress). Depending on your printer calibration, you may need to do some minor filing.
The default parameters (and sample STL) make one side much tighter than the other (so it stays on and doesn't get lost as often as the original, hopefully). In the pictures I simply marked the looser end with a label printer.