Okay I figured it out.
I asked on IRC ##linux if there was a way to run scripts on startup, on any Linux distro and any desktop environment.
To achieve it, one needs to create a launcher (a .desktop file) - and place that file in /etc/xdg/autostart and then in the file properties of the launcher you can make it run a command to run your script. The command should look like this:
sh -c '/usr/local/bin/myscript.sh &'
Myscript.sh needs to be made executable, this can be done in Xfce via the file properties. (allow the file to run as a program)
It’s generally good practice to place regular scripts in /usr/local/bin and sudo scripts in /usr/local/sbin . (scripts made by the user/you)
In this way you can run scripts on startup, on any Linux distro and any desktop environment.