In caja it seems there is no way to add a folder to the Places menu. I tried caja help menu > F1 but didn't get anywhere. Any help would be appreciated.
This is in caja 1.20.0
in your home folder, inside .config theres a file called user-dirs.dirs, just edit that file to your liking. Heres a copy of mine
XDG_DESKTOP_DIR="$HOME/Desktop" XDG_DOWNLOAD_DIR="$HOME/Downloads" XDG_TEMPLATES_DIR="$HOME/Templates" XDG_PUBLICSHARE_DIR="$HOME/Public" XDG_DOCUMENTS_DIR="$HOME/Documents" XDG_MUSIC_DIR="$HOME/Music" XDG_PICTURES_DIR="$HOME/Pictures" XDG_VIDEOS_DIR="$HOME/Videos"
Another method besides what @christian mentioned that does not require config file edit is to add the folder as a bookmark:
After you added a folder to the bookmarks, you will be able to drag-and-drop additional folders by dropping them on the Bookmark label.