I combined my favorite cart coin model (https://www.printables.com/model/124639-cart-coin-keychain) with a great quick-release key chain from mistertech on Thingiverse (https://www.thingiverse.com/thing:3545673). I've made male & female versions of the cart key. The corresponding files for the key chain end ("small" size) can be downloaded at the Thingiverse link.

The cart key should probably be printed with 4 or 5 perimeters for extra strength. However, the female end of the quick-release requires some flexibility, so I'd recommend using the male version of the cart key (with 4+ perimeters) & the female end of the key chain (~2 perimeters). The quick-release mechanism gets smoother with use. The cart key has been tested in US ALDI carts.