If the current document is Untitled, New File, No Name, etc and does not actually point to a file, then the ubiquitous Floppy icon should act as Save As. Once the file does exist, a simple Shift-click of the same floppy icon should also act as Save As. Same thing as Cmd-S/Cmd-Shfit-S. However, I'm unfamiliar with this modifier click save as from any app.