Google's Advanced Search Operators
Google's Display Planner
The Inspect Element of any given URL ( I don't think it's a tool but I use this all the time and then control F search the exact thing I'm looking for)
Google's related searches at the bottom of queries
AWStats ( in Cpanel)
Built With (to spy on competitor's CMS, plugins, etc)
Notepad Light (to make changes to files and then uplaod them to the server via FTP)
I could possibly live without them, but I still would not be happy about losing the following:
Whitespark (for Local SEO)
Wordtracker Scout Chrome Extensionhttps://inbound.org/article/the-seo-tools-we-couldnt-work-without
http://www.jamesbachini.com/misc/guestpostrequest.php