Son Do

Floating Publish Button is perfect especially for editors who use the page and post editing interfaces more than regular administrators.
They’ll find this plugin extremely useful, since there won’t be any need to scroll up and hit Publish/Save every time they want to update the post, especially if it’s a really long post or a page with lots of metaboxes.
If this behavior is annoying for some users, it can easily be turned off from the user’s backend profile page.
<ul>
<li>Enable/Disable settings in Admin > Users > Your Profile > Publish/Update button</li>
</ul>

Floating Publish Button

I'm working on a site with ACF custom fields to add sponsor logos to pages.  Some pages have dozens of sponsor logos so the pages get very long.  Having to scroll to the top of the page to update was a pain, but this plugin keeps the Publish metabox in sight.  And it still works in June 2017 :D

Still working :D

Should be in core

A WordPress plugin that alters the position and behavior of the Publish button, making it stick to the top of the page when scrolling down the page

meloniq

Enables searching post meta fields on admin pages.

WP-Admin Search Post Meta

Enables searching post meta fields on admin pages.

Floating Publish Button vs WP-Admin Search Post Meta