Keep Cart: For Zen Cart v157 and later (including v158)

This drop-in plugin keeps a guest customer's cart in a browser-based cookie. Once the customer has logged into your store, their selections are maintained in your site's database.

It's been tested on Zen Cart 1.5.7c (but should work on any fully-patched zc157 installation) and Zen Cart 1.5.8. The plugin requires a minimum PHP version of 7.3.0, since that PHP version introduced the support for samesite cookie controls.