WooCommerce plugin which adds a checkbox on each product which will prevent coupons applying to that product. Any coupon a customer uses will still apply to all other items in the cart.
The code is a slightly modified version of a StackOverflow answer to Exclude product from all coupons in WooCommerce.
If the plugin Search by ID has been installed, the "Products" link on plugins.php will link to the list of products that have the setting enabled.
Download from GitHub releases.
See github.com/BrianHenryIE/WordPress-Plugin-Boilerplate for initial setup rationale.