Sy's Peglock universal board attachment, modified to fit the thin metal pegboard on this cart from target.

The pegboard on this cart seems to be a 25mm grid of 6mm holes, compared to the 25.4 and 6.25 (1"x1/4") pegboard standard the original was designed for. It's also only about 2mm thick, making the pegs much shorter and tighter to the body of the model.

It's probably possible to snug it up more tightly but I don't know how common this particular kind of pegboard is, and it's serviceable for me at this state.