Do you want your app launcher to just be a button on the panel bar that launches one app when you click on it? If so, then you should be able to:
1. Right click on the panel bar and select "Add to Panel"
2. Select "Custom Application Launcher" then click "Add".
3. Fill in "Name:" and "Comment:" with some reminder text or a name.
4. Fill in "Command:" with the name or path to the application, plus any customizing options.
5. Clock on the springboard icon and browse for a different icon to be displayed.
If, instead, you want a custom menu to come up, with your applications listed in this menu, then I suggest getting the source code to the "myGtkMenu" program at ...
... unless you can find it in your package repository. This package is technically an app, but uses the Gtk+ API calls for menus to implement a menu (is styled just like a menu, goes away when an app is launched, etc). It then uses a menu configuration file in its own format. You would still use the steps I gave above to get it onto your panel bar, but you would specify the myGtkMenu program and menu config file name as the launched command. For example, I created such a menu for websites I visit often. In the app launcher I set up:
Command: /usr/local/bin/myGtkMenu /home/phil/.myGtkMenu/Websites
and gave it the "fox globe" icon. Then I have a big file as named on the command line with a configuration similar to the example file included in the source.