clear-unused.php - helps you to remove a lot of unused modules from Wordpress (for example, emoji). Add to functions.php
hide-acf-totally.php - helps you to hide ACF from admin menu, hide gear of ACF on pages, do redirect from ACF pages
selflink.php - helps you to avoid selflink for wp_nav_menu objects without breaking of CSS (very useful for SEO)
wp-mail-with-attachments.php - helps you to know how to use wp_mail function with attachments if your file is uploading locally
wp-mail-with-attachments-ajax-handler.php - function of ajax handling for form which has input[type="file"]