I use an org file as my journal. The top headings are the current date and the child headings are the entries for that day. I put everything in there - interesting things I find, TODOs, things I've worked on, random thoughts, and even foods I've eaten. I also keep a rough drafts of my reading summaries for the day before transferring them to their appropriate org files.

I've added a convenient way of opening my journal from anywhere in Emacs:

(defun my/open-journal-file ()
  "Open journal.org file."
  (interactive)
  (find-file "~/org/journal.org")
  ;; Go to the last line of the file
  (evil-goto-line)
  ;; Go to the last top level heading
  (re-search-backward "^\\* ")
  ;; Reveal text immediately after the heading
  (org-fold-show-entry)
  ;; Reveal children of the heading
  (org-fold-show-children)
  ;; Go to the last line of the file
  (evil-goto-line))

This opens the journal, expands the last date, and puts me at a location where I can add a new entry.

My journal goes all the way back to 2023.