With Rereplacer I added my own tags (#sub#) and had those replaced with HTML tags (). So H#sub#2#/sub#O becomes H2O.
So thanks to this extension my customer now can have chemical formulas in their article titles & menu items. Thanks!
Akeeba Backup saves you time & hassle with creating back-ups of your website.
And with Akeeba's restore tool "kickstart.php" you can easily restore a backup. I'd also recommend to use that tool to create test environments on other (e.g. local) servers for testing purposes.
You can optimize the editor button bar from usability point of view so that your site's editors only have the buttons they need. E.g. I'd recommend to remove the font chooser & color buttons: use CSS styles instead! It will save you time when you change the template in the future (and you won't have to change all hard coded font settings from your articles).
btw: I also use the commercial JCE addons from the same developer which make it easier to add photos & documents to your content.