I would say it heavily depends on what you are doing with the editor. If you use it for web development, there would be different packages of interest, than what might be useful for example if you work on a C++ project.
You could checkout the search or the labels on the https://packagecontrol.io/browse website to look for interesting packages. But I would also take a glance at the GitHub repo (usually) of the package, if you found one that looks interesting, to see whether it is still maintained.
If you want to use the editor to work on a bigger project, perhaps the LSP package might be useful to you if there is a language server for the programming language you use (usually there exists one), to provide some additional features which can usually be found in IDEs. But if you use the editor to just quickly edit some files, then maybe something like that is not necessary or useful to you. We can only guess without further information.
There is a built-in “Open containing Folder…” item in the context menu when you click on a file in the sidebar, but only under the “Folders” section of the sidebar (if you have opened a folder or project in Sublime Text) and not under the “Open Files” section.
If you want to edit the sidebar context and/or add your own functionality via the plugin API, the relevant file for file entries is Side Bar.sublime-menu
, see also https://docs.sublimetext.io/guide/customization/menus.html#available-menus.