How can I modify the panel (in classic Gnome mode) such as adding items, moving, etc. in Ubuntu 12.04?
I had the same problem with an earlier version of Ubuntu here, which received an answer to press Alt while right clicking, and it worked for that version, but this does not seem to work for 12.04.
The following keyboard combination worked for me on Ubuntu 12.04: Super(Button with windows logo on it)+Alt+Right Mouse Click.
I'll try and help you here - do you mean graphically like with the alacarte menu editor? It's really straightforward to use.
You access this tool by right clicking the menu area (upper left) in GNOME and selecting “Edit Menus”. When you do this the menu editor will open.
I have not figured out how to post pictures yet, so if you do not come right, lemme know.
Hope this helps