The easiest thing I know to do is add a 'drawer' and stick the items you want in there.
right click on the panel, select 'add to panel', select 'Drawer'.
then left click on drawer to open it and right click on the bottom part of it to add items. Or open up the drawer and drag and drop the items you want into it.
The drawer is basicly like a entire new panel and you can add items to it and such.
It's not quite the same as adding a new entry to the applications menu, but it's close, I figure.