Here are some of the plugins I use in most (or at least many) of my sites:

Yoast SEO

Excellent SEO plugin, with (almost) everything you will need (link)

W3 Total Cache

Speeds up your site (link)

Contact Form 7

Create simple contact forms (link)

Contact Form to Database

Save all contact form submissions to database (so nothing gets lost) (link)

Akismet

Cleans 99% of spam (link)

Wordfence Security

Extra security for your site (link)

Pretty Link Lite

Add website redirects, and track clicks. (link)

WP Offload S3 Lite

Store the images on your site in an Amazon S3 bucket. Save space and bandwidth. (link)

Updraft Plus

Automatically (and/or manually) create a backup of your site (link)

Google Analytics Dashboard for WP

Add Google Analytics tracking. Does what it says. (link)

BONUS: 2 other plugins that I have used in the past multiple times (also free)

Woocommerce: eCommerce solution for WP

BuddyPress: Turn WordPress into a Social Network

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