Adrien Brochard over at Xmodulo has a list of 10 productivity packages for Emacs. Some of them are actually built-ins but they're all something that every Emacs user should consider installing or using. I'm a user of almost all of them and wouldn't want to live without them.
One that I'm not using is auto complete but Brochard's writeup has convinced me to give it a try. With ELPA it's trivial to try a package out and revert it if it doesn't work for you.
I won't ruin your Christmas surprise by revealing the rest of Brochard's list so you'll need to follow the link. Really, there's no reason you shouldn't be using—or at least seriously consider using—these packages. They can help speed you on your way to being an Emacs master.