In more or less random order:

• Org-Mode is one of the most amazing packages for Emacs. Some people use Emacs only for that. I personally use it for second-brain style note taking, TODO lists, simple presentations, PIM, Wiki-like articles, writing docs (and then exporting it to other formats), and even some simple integrated spreadsheets/tables including some simple calculations
• Magit is a really good Git frontend. Some people use Emacs only for that.
• Use “use-package” to install/configure packages. Streamlines configuration a lot, compared to the old days.
• Use the “no-littering” package to move a lot of randomly generated files into centralized directories
• Use winner mode to undo/redo window configuration changes
• Use which-key to show a popup of available keybinds when typing something
• Use the integrated “time” package to create a world clock view
• Use the integrated modus-themes for highly configurable themes with a nice contrast (since I’ve spent some time configuring that theme, I’ve stopped using any other theme)
• Use hl-todo package to highlight keywords like “TODO”, “NOTE”, “WARNING” or “DONE”
• Use doom-modeline for a nice modeline
• Use nerd-icons to add nice icons to many views
• Use avy to quickly jump to specific locations, lines or characters using different keystrokes
• Use eshell for a quick shell (which works the same on every Emacs, regardless of the OS) and/or either vterm or eat if you need a full-fledged terminal emulator
• Use embark as a “context menu” when cursor is over anything (bind embark-act to e.g. “C-.”)
• Use editorconfig package to specify/load different editor configs per project
• Use treesitter and eglot (or lsp-mode) for modern syntax parsing using language servers
• Use neotree (or treemacs?) as a file tree viewer, but dired is also cool if configured well
• Use org-modern package to beautify org mode display
• Use org-appear to hide formatting characters unless cursor is directly next to them
• Use Unicode characters to beautify otherwise ugly or bland default characters, e.g. set " ▾" for org-ellipsis
• Use gcmh or similar packages or config settings to improve general Emacs UI responsiveness
• Use packages which improve the minibuffer, buffer switching, completion, and basic things like that. There are several good ones and you can’t really go wrong with any, I just think the newer, more well-integrated ones like consult, vertico, orderless, marginalia, and so on are “nicer” than the older less well-integrated ones like helm, ivy and so on
• Bind “goto-last-change” to a nice keybind
• Bind “quick-calc” to a nice keybind
• Bind “org-agenda” to a nice keybind
• Bind “toggle-truncate-lines” (line wrapping) to a nice keybind
• Bind “kill-this-buffer” and “kill-this-buffer-and-window” to nice keybinds (e.g. C-x k / K)
• Bind “consult-line” (or something similar) to e.g. C-s
• Bind all window and buffer cycling/management related commands to nice keybinds
• If you want an easier entry into Emacs and are already a Vim user, try the Doom Emacs distribution. If you want to start with Vanilla GNU Emacs but want a decent but minimal default configuration, try emacs-bedrock.