Right click a toolbar, choose Customize. I have a couple of sets of extra buttons (extensions for them). Since I use Tiny Menu, I have plenty of room for the address bar and search bar on the main toolbar, plus three other buttons (paste and search, customize toolbar, SmileyXtra). I moved all my navigation buttons to the bookmark toolbar, along with the FEBE button, translate button, and preferences button.
I used the sidebar for everything else... Add tab, bookmarks, downloads, CookieCuller, extensions, Wikipedia, add bookmark, bookmark manager, Firebug, and Search. All the icons on the bottom were put there by extensions, not me.
Notice that I do not have the navigation toolbar in use because I moved the buttons from it to the other bar. I've kept this configuration for a while now because it suits my needs.