Comment 28 for bug 32194

On my ubuntu 7.04 the gnome-session-properties is sorted by the Name given to the session entry. Changing the name changes the sort (so you could perpend a numeric entry to force a sort.

The files created are stored in:
~/.config/autostart

and follow the desktop entry spec: http://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html

[Desktop Entry]
Version=1.0
Encoding=UTF-8
Name=No name
Name[en_US]=gnome launch box
Exec=gnome-launch-box -n -t
X-GNOME-Autostart-enabled=true

I will check if changing the sort by altering the entry Name actually changes the launch order.