I'm not an optimization expert nor am I a WP power user but I have been using the platform for over ten years.  I have a strong preference for plugins that are lightweight, easy-to-implement and configure, and have a clean removal (plugins which leave artifacts are a huge pet peeve of mine).  Here's a list of my must-have plugins for almost all WordPress installations.

WordFence

My complaints with WordFence surround it's initially annoying push for upgrading to the premium version. You can dismiss/hide those, though, which leaves you with a pretty effective solution at thwarting most low-end abusive crawlers/sniffers. The highlight is the threshold with auto-block feature which allows you to block traffic if activity breaches certain thresholds.  It just makes things easy. https://wordpress.org/plugins/wordfence/

Instant Images

Although not my area of interest, it's handy.  Instant Images pulls free-to-use (under the CC0 license) images from UnSplash directly into your WordPress media library.  It saves a few clicks and makes things easier when in need for stock images. https://wordpress.org/plugins/instant-images/

Velocity

Velocity is a nifty plugin that allows you to embed YouTube/Vimeo/SoundCloud media without loading the heavy iframes/JS libraries until the user engages with the media.  This saves a ton on overall load time/size.  It also allows you to set a custom preview image for your embedded media so that's a small plus.  Using this plugin, I reduced my page load size from 1.73mb to 634kb and reduced the number of requests onload from 89 to 59 -- this is a 1 second decrease in pageload for devices on 3G networks! https://wordpress.org/plugins/velocity/

commonWP

commonWP is a plugin which uses the jsDelivr CDN for common WordPress JS files.  It's super easy and low-risk to implement thanks to really well thought out work from the creator.  I hope this expands to CSS files in the near future. https://wordpress.org/plugins/commonwp/

Enlighter

Enlighter is an easy-to-use syntax highlighter that supports most languages.  While there are several syntax highlighters out there, I like this one in particular for it's easily modifiable CSS and clean editor integration. https://wordpress.org/plugins/enlighter/

WP Mail SMTP

As the name suggests, this plugin enables easy use of SMTP for mail on your WordPress installation.  No need to go deeper than your WP-Admin pages to configure mail for your WordPress installation.  The downside is that it was recently acquired by WPForms so I'm guessing it'll be turned into an intrusive, premium-hocking version in the near future. https://wordpress.org/plugins/wp-mail-smtp/