What should be disabled to run on an internal network with no access to the Internet?

After more fruitless searching, I stumbled across this article from WP Tavern which mentioned a plugin then called “WP Local Dev Environment,” now called Airplane Mode. The plugin blocks a long list of things that WordPress does which require checking something from the Internet.

While it is intended to be toggled on or off depending on whether you have a connection, I can use it in perpetual “on” mode on my internal network sites. After enabling, pages that were taking 15-30 seconds to load now load almost instantaneously. BRILLIANT!

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)