1- Contact Form7
Contact Form 7 can manage multiple contact forms, plus you can customize the form and the mail contents flexibly with simple markup. The form supports Ajax-powered submitting, CAPTCHA, Akismet spam filtering and so on.
2- All In One SEO Pack
Use All in One SEO Pack to optimize your WordPress site for SEO. It’s easy and works out of the box for beginners, and has advanced features and an API for developers.
3- Classic Editor
Classic Editor is an official plugin maintained by the WordPress team that restores the previous (“classic”) WordPress editor and the “Edit Post” screen. It makes it possible to use plugins that extend that screen, add old-style meta boxes, or otherwise depend on the previous editor.
CMB2 is a developer’s toolkit for building metaboxes, custom fields, and forms for WordPress that will blow your mind. Easily manage meta for posts, terms, users, comments, or create custom option pages.
5- CMB2 Tabs
CMB2 Tabs is an extenstion for CMB2 which allow you to oragnize fields into tabs.
CMB2 Tabs Extension requires the most current version of the CMB2 plugin.
6- One Click Demo Import
The best feature of this plugin is, that theme authors can define import files in their themes and so all you (the user of the theme) have to do is click on the “Import Demo Data” button.
7- Redux Framework
Redux is a simple, truly extensible and fully responsive options framework for WordPress themes and plugins. Built on the WordPress Settings API, Redux supports a multitude of field types as well as: custom error handling, custom fields & validation types, and import/export functionality.
8- WP GDPR Compliance
This plugin assists website and webshop owners to comply with European privacy regulations known as GDPR. Activating this plugin does not guarantee your site fully complies with GDPR.