1- Contact Form 7

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. Contact Form7

2- 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. Classic Editor

3- CMB2

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. CMB2

4- 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. One Click Demo Import

5- 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. Redux Framework