Hi,
can't believe this thread slipped me for so long...
Well, after some 6 years in (X)emacs and with a configuration of some 4000 lines of elisp I must have configured my XEmacs (almost) exactly to my needs. What is it that makes this so powerfull for me?
dabbrev (defaults to M-/): dynamic abbreviations which lets you pick the really long but insightful variable names because you don't have to type them anymore.
M-x locate so you'll never do the locate in xterm and mark the filename with the mouse again (later pasting that filename into XEmacs anyway)
speedbar one of the finest tools for navigation in large projects I've ever come across
desktop for re-opening all the files on the next day
active-menu.el (see the website) for one more line of code
function-menu for another navigation mechanism which works only in the current buffer (a buffer is usually a representation of a file in the editor)
saveplace to find myself at exactly the cursor position as the last time I opened that file
cperl auto help shows a short syntactic information; good if it has been a while since your last perl programm
and thousands of other things that don't spring to my mind in this moment