I'm not very familiar with GNOME; I use KDE. There might be some "good" way to rebuild a fully functional GNOME panel, but I only know the way I figured out that works.
Like you, I accidentally deleted my GNOME panel. I don't really remember how I did it, but anyway there I was stuck without a panel. I right clicked and added a panel, and like you I got a blank panel which didn't actually "do" anything. After that I right clicked on the blank panel and fiddled around to add various "stuff" to it, like a taskbar and menu and clock and such.
So, the solution I know is to use trial-and-error to add stuff to the panel until eventually you get something with acceptable functionality. Maybe there's some good solution for simply reseting the panels to the default, but I don't know it.