This is a subjective list of my personal favorite WordPress plugins; some I use on every single WordPress site I develop, and some, although not always needed, I think are great plugins with great development teams behind. Probably don’t install them all, but if you think you can use one of them, you can’t go wrong with these:
WP Super Cache is a simple and reliable cache option. Alternatively: Cache Enabler is even lighter and quite fast. And with WP2Static you can output a completely static site (if you know what you’re doing).
Better Search Replace for easily making quick search/replace changes on the database
HTML Forms for simple forms, with flexibility to make them just as you want them. Alternatively: Contact Form 7 doesn’t have the best code base, but it’s easy to find support for anything you need to do.
Stream for tracking changes on a WordPress install, specially on a client site.
Really Simple SSL make the site run on https without headaches. Particularly useful when taking over an old site.
UpdraftPlus for making backups.
Classic Editor, because I don’t think Gutenberg is ready for most users yet. This one is a personal preference.
And a custom functionality plugin, for any theme-agnostic script I need to include, like custom post types and taxonomies.