The emacs function that seems nifty to me at the moment is hippie-expand. It is bound to the key sequence M-/. Unless I set that up specially, it is probably bound the same way in your emacs environment. Below is its documentation, which can be obtained with M-x describe-function hippie-expand.

hippie-expand is an interactive compiled Lisp function in `hippie-exp'.
(hippie-expand ARG)

Try to expand text before point, using multiple methods.
The expansion functions in `hippie-expand-try-functions-list' are
tried in order, until a possible expansion is found.  Repeated
application of `hippie-expand' inserts successively possible
expansions.  
With a positive numeric argument, jumps directly to the ARG next
function in this list.  With a negative argument or just C-u, 
undoes the expansion.

Have fun!