Create a application starter in your tint2 panel

First install xdotool:

#pacman -S xdotool

Add this line in the keyboard section of your ~/.config/openbox/rc.xml

   root-menu
 

We do
$openbox --reconfigure
to update openbox menu
 Check if this works with
 $ xdotool key ctrl+alt+space
You should see the OB menu pop up near your mouse.

Now we install tint2-svn from AUR with yaourt or packer
$yaourt tint2-svn

After installing we edit the tint2rc by hand in /home/username/.configure/tint2
Under panel we add:
# Panel panel_items = LTSBC

 And we add a new section:
# Launchers
launcher_icon_theme =Adwaita
launcher_padding = 5 0 10
launcher_background_id = 9
launcher_icon_size = 85
launcher_item_app = /usr/share/applications/tint2.desktop

Now we are going to create the  tint2.desktop file in the folder  /usr/share/applications
Create a file nameit tint2.desktop and with leafpad add the text and save:

[Desktop Entry]
Categories=Panel
Comment=A menu launcher
Exec=xdotool key ctrl+alt+space
GenericName=tint2
Icon=tint2
MimeType=
Name=tint
Type=Application
X-KDE-StartupNotify=false


 Now we kill tint2 with
 $pkill tint2
 And activate it again with dmenu, alt-f3,type tint2 and enter.

If all is good you should see this: