Is there a single shortcut to start inserting in the new line at end of the file? I'm aware of G + o combo.
Not that I know of - G + o is what I would have suggested too, but that is 2 steps :)
You could always create a macro which does G + o, and then you can invoke the macro which will be 1 step.
Adding the following into ~/.vimrc will create one for you:
:nmap ^A Go
To type the "^A" first press Ctrl-V, then press Ctrl-A. You can then use Ctrl-A to append at the end of the file when not in insert or visual mode.
You could stick the map definition in your .vimrc and then invoke it when the you open the file.
Or, if you only want to do this for a particular file, you could create an autocmd for that file type that does it automatically. See autocommand in the vim doc's.
HTH
cheers,
Rob
There's also the command line option "+":
vim + myfile.txt
Will open myfile.txt and do an automatic G for you.