After working on over thousand WordPress web sites I found that these nine plugins are essential for almost every WordPress setup. All other plugins are needed per site basis and no matter how much those can be useful not every site needs them.
Get rid of the new and modern block editor with this plugin.
Industry standard. Little bit bloated but luckily you can disable most of the unnecessary stuff.
This plugins generate html and only html sitemap in a page you created and inserted shortcode. It is useful to show of site sitemap to your visitors. It complement Arne’s plugin very well.
As soon as your site grows you will need this. With the help of conditional tags you can display your widgets only on certain parts of your site (etc certain posts, category, frontpage or attachment).
Every site needs proper contact form. This plugins makes that task very easy. Generate your form and insert it with the shortcode where you need it.
Plugin with unique “related” detection algorithm. It support custom types posts too and its own template system.
Ex: Quick Cache and Zen Cache. Fasten your seat belts. This plugin caches your whole site and serve your visitor cached version of the same. This reduce loads and speed loading of the web site. It works perfectly with the Autoptimize.