You can customise the right-click/context menus via: Tools → Customise… → Context Menus
I've found it useful to add my own styles to this list, for example (Select 'Styles' from the 'Category' drop-down to get more options).
You can customise keyboard shortcuts via: Tools → Customise… → Keyboard. I've had issues with Calc settigns not overriding LibreOffice ones, but it's still useful. Made it easier to paste unformatted text, for example.